The Church of the East: Christianity’s Forgotten Fourth Branch

"And let thy Holy Spirit come, O my Lord, and rest upon this offering of thy servants, and bless it and sanctify it that it may be to us, O my Lord, for the pardon of sins, and for the forgiveness of shortcomings, and for the great hope of resurrection from the dead, and for new life in the kingdom of heaven, with all those who have been pleasing before thee."

— Epiclesis from the Anaphora of Addai and Mari, the Church of the East’s most ancient Eucharistic prayer, as reproduced in the Pontifical Council for Promoting Christian Unity, Guidelines for Admission to the Eucharist between the Chaldean Church and the Assyrian Church of the East (Vatican City, 20 July 2001)

The Fourth Branch of Christendom

When Western Christians speak of Christianity’s great divisions, they typically invoke three historic separations: the East-West schism of 1054 (splitting Orthodoxy from Catholicism), the Reformation of the sixteenth century (fragmenting Western Christianity), and, for the more knowledgeable ones, the split at the Council of Chalcedon (451) that created the Oriental Orthodox churches. But there is a fourth, often overlooked: the Church of the East, which separated at the earlier Council of Ephesus (431) yet remained geographically distinct from both the Byzantine East and the Latin West, maintaining its own apostolic succession, liturgy, theology, and missionary expansion for two thousand years.

The Church of the East is Christianity’s forgotten fourth branch—not Eastern Orthodox, not Roman Catholic, not Oriental Orthodox, but sui generis, a living apostolic communion that at its medieval zenith spanned from the Mediterranean to Beijing, with more metropolitan sees than Rome itself. That it is unfamiliar to most Western Christians is a historical tragedy. Its story is one of apostolic fidelity, missionary audacity, theological sophistication, and martyrological endurance. It remains, in our own time, a small but vital witness to the catholicity of the Christian faith.

The table below shows how the Church of the East sits in relation to the three branches Western Christians more commonly recognize.

The Church of the East is the only one of the four whose decisive break came at Ephesus rather than Chalcedon or 1054, and the only one whose theological vocabulary (parsopa, qnome) sits outside both the Greek and Latin philosophical traditions. The result is a tradition whose Christology is in substance dyophysite—the same two-natures doctrine Chalcedon defended—expressed in Antiochene terms that the 1994 Common Christological Declaration between Rome and the Assyrian Church formally recognized as orthodox.

Apostolic Origins: The East Syriac Tradition

Mesopotamia and the Eastward Vocation

The Church of the East claims apostolic origins in Mesopotamia, the ancient heartland between the Tigris and Euphrates rivers. Christian tradition ascribes its founding to three apostles: Thomas (who, legend holds, evangelized India and Mesopotamia before his martyrdom), Thaddeus (also called Addai), and Mari.

Unlike the churches of Jerusalem, Antioch, or Alexandria, which developed within the Mediterranean Roman Empire and were shaped by Greek philosophical categories, the Church of the East developed in the Sassanid Persian Empire, drawing on Aramaic linguistic and theological traditions. Its liturgical language is East Syriac, a dialect of Aramaic so close to the language Jesus himself spoke that modern scholars studying the Church of the East’s theology often feel they are hearing echoes of first-century Jerusalem itself.

The church’s early ecclesiastical center was at Seleucia-Ctesiphon, the Persian capital (modern Iraq), where a metropolitan see was established early in the Christian era. Unlike the bishops of Rome, Constantinople, Jerusalem, and Alexandria—the four patriarchs of the Mediterranean world—the catholicos (patriarch) of Seleucia-Ctesiphon governed a church that faced eastward, toward the vast unmissionized lands of Central Asia, India, and the Far East.

The Liturgical Foundation: Addai and Mari

At the spiritual heart of the Church of the East lies one of Christianity’s most ancient and theologically profound liturgies: the Liturgy of Addai and Mari, still in use in the church today. This Eucharistic prayer is remarkable for its antiquity and its singular theological content. Dating to the fourth century or earlier, it stands as a monument to the church’s continuity with apostolic practice.

Most striking to modern liturgists is the way the Anaphora (Eucharistic prayer) handles the institution narrative—the words of Christ at the Last Supper (“This is my body… this is my blood”). Unlike most other historic Eucharistic prayers, Addai and Mari does not recite these words in a single, continuous narrative. Instead, as the Vatican itself observed in 2001, the words of institution are present “not in a coherent narrative way and ad litteram, but rather in a dispersed euchological way”—woven throughout the prayer alongside the memorial of Christ’s entire redemptive work, the epiclesis (invocation of the Holy Spirit), and the remembrance of the church’s communion with heaven. For centuries, Roman theologians had questioned whether a Eucharistic prayer lacking the customary narrative formula could effect a valid consecration. In 2001, the Vatican formally recognized the Liturgy of Addai and Mari as a valid Eucharistic prayer, concluding that its dispersed presentation of the dominical words satisfies the requirement that the words of institution be present and operative in the consecration.⁠¹

This recognition signified something profound: that the Church of the East’s ancient practice, developed independently of Rome, embodied orthodox sacramental theology and was worthy of recognition as authentically apostolic.

The Christological Controversy and the Council of Ephesus (431)

To understand the Church of the East’s historical identity and the “Nestorian” epithet that has dogged it, one must grasp the great Christological controversies of the fifth century.

The question was deceptively simple: How are Christ’s divinity and humanity related? Is He one person with two natures? Two persons in one union? One nature that combines divine and human? The answers seemed to determine not only Christology but the entire structure of salvation itself.

The Antiochene Theological Tradition

The Church of the East inherited the theological tradition of Antioch, which emphasized the distinction between Christ’s divine and human natures. The great Antiochene theologians—Diodore of Tarsus (d. c. 390) and especially Theodore of Mopsuestia (d. 428)—taught a dyophysite (two-nature) Christology that stressed that in Christ, the divine Word and the human nature remained truly distinct, united not by confusion or fusion but by a perfect union of will and action.

This tradition was not heretical. Theodore and Diodore were orthodox theologians. Yet their insistence on maintaining the distinction between natures, their emphasis on Christ’s human will and agency, and their caution about language that seemed to blur the boundary between divine and human, would become the bone of contention.

Nestorius and His Formulation

Nestorius, patriarch of Constantinople (428–431), inherited this Antiochene theological sensibility. When Nestorius heard Christians addressing Mary as Theotokos (God-bearer or Mother of God), he recoiled. To call Mary the mother of God seemed, in Nestorius’ view, to confuse the divine and human natures. Was not God eternal and immutable? How could He have a mother?

Nestorius insisted on precision: Mary was the mother of Christ (Christotokos), the mother of the human nature, not the mother of the divine Word. He seemed to teach—though the exact extent of his teaching remains debated—that Christ consisted of two distinct persons loosely united, rather than two natures in one person.

The Council of Ephesus (431) and Condemnation

Cyril of Alexandria, theologically opposed to Nestorius and invested in defending the Theotokos title, pressed for an ecumenical council to condemn Nestorius’ teaching. In 431 AD, the Council of Ephesus convened. Cyril dominated the proceedings. The council condemned Nestorius, declaring that Christ is truly one person, that the Word did indeed assume human nature, and that Mary is rightly called the Theotokos.⁠²

Yet Ephesus was not a purely theological triumph. The council was marred by procedural confusion, the absence of some key bishops, and—most significantly—by Cyril’s own theological language, which seemed to many (especially Antiochene theologians) to verge on monophysitism, the teaching that Christ has only one nature (the divine absorbing the human).

The Church of the East, governed from Persia outside the Roman Empire, rejected the council’s terms. Not because they believed in two persons in Christ, but because the council’s condemnation of Nestorius seemed to them to rest on misunderstandings and because they found the council’s own language (especially Cyril’s) suspicious. They preferred to maintain their own Antiochene vocabulary: two natures, united in one person (or prosopon, roughly “face” or “persona”).

Modern Scholarly Consensus

Here a crucial point must be emphasized: the modern scholarly consensus, crystallized in the 1994 Common Christological Declaration between Pope John Paul II and Mar Dinkha IV (the patriarch of the Assyrian Church of the East), recognizes that the Church of the East was never truly “Nestorian” in the heretical sense.

The declaration states: “Whatever our christological divergences have been, we experience ourselves united today in the confession of the same faith in the Son of God.”⁠³ The church teaches an orthodox two-natures Christology; it simply uses different terminology (East Syriac kyane for natures, close to the Greek physeis/ousia, and qnome for the concrete subsistences or individuated instances of those natures, functioning much like the Greek hypostasis) that was easily misunderstood by Western theologians.

The “Nestorian” label, imposed by polemicists and perpetuated through centuries of ecclesiastical politics, was fundamentally a misnomer.⁠⁴ The Church of the East does not hold that Christ is two persons; it holds that Christ is one person with two natures, united in an unconfused, inseparable union—which is precisely what Chalcedon (451) also taught. The difference lies in vocabulary and hermeneutical tradition, not in fundamental doctrine.

Three Dates, Three Different Events: 410, 431, 484

Popular accounts often telescope the Church of the East’s emergence as a distinct communion into a single moment at Ephesus 431. The historical reality is three distinct events. 410 marks organizational independence: the Synod of Mar Isaac at Seleucia-Ctesiphon proclaimed the Catholicos’s primacy across the Sassanid Persian Empire and formally adopted the Nicene Creed and Nicaea’s canons, and the Synod of Dadyeshu (424) extended this by declaring that the Persian Catholicos was answerable only to the tribunal of Christ. 431 marks the doctrinal trigger: the Church of the East simply did not receive the Council of Ephesus, partly because it stood outside the Roman imperial system that called the council and partly because Cyril’s victorious formulations seemed (to Antiochene readers) to verge on monophysitism. 484 is the formal Christological turn: the Synod of Beth Lapat, convened under Barsauma of Nisibis, adopted the Antiochene dyophysite tradition associated with Theodore of Mopsuestia as the church’s doctrinal standard. The Synod of Mar Aqaq two years later (486) reinforced this with strictly dyophysite formulations, anathematizing any teaching that “suffering and change apply to the divinity of our Lord.” It is 484 and 486, more than 431, that gave the Church of the East its mature theological identity.

The Extraordinary Missionary Expansion

If the Church of the East’s theological sophistication is underappreciated, its missionary achievement is virtually unknown in the West. Yet between the fifth and fourteenth centuries, it undertook the most expansive missionary effort in pre-modern Christianity, spanning continents and converting vast populations from Central Asia to China.

The Silk Road Missions

From its base in the Sassanid Empire, the Church of the East began, in the fifth century, to push eastward along the caravan routes we now call the Silk Road. Monks and missionaries established monasteries at key trading posts, baptized local populations, and gradually established metropolitan sees across Central Asia, India, and beyond.

By the seventh century, the church had reached China. In 635 AD, a missionary named Alopen arrived in Chang’an (modern-day Xi’an), the capital of the Tang dynasty. The Tang emperor, Taizong, was intrigued by this foreign faith. A century and a half later, in 781 AD, a magnificent limestone monument was erected in Chang’an to commemorate the arrival of the “Luminous Teaching” (as the Chinese called Christianity). This Xi’an Stele, as it is known, provides a detailed account of Christian doctrine, Christ’s redemptive work, the sacraments, and the church’s liturgical life—all translated into classical Chinese.⁠⁵

Metropolitan Sees and Geographic Reach

At its medieval apex, the Church of the East possessed an astonishing geographic footprint. It maintained:

• Metropolitan sees in India, including the famous St. Thomas Christian communities of the Malabar Coast, which claimed apostolic succession from Thomas the Apostle himself
• A metropolitan see in Samarkand (Central Asia)
• Extensive communities in Persia and Mesopotamia
• Presence in Tibet, where Nestorian Christianity competed with Buddhism for influence
• Multiple communities in Mongol domains, including the Khan’s court itself
• A thriving presence in China, where the Tang state initially called the religion the “Persian Religion” (波斯教 bōsī jiào) because its missionaries had come via Persia; after a 745 imperial edict by Emperor Xuanzong, the official designation was changed to the “Luminous Teaching of Daqin” (大秦景教 Dàqín jǐngjiào), which was the Christians’ own preferred self-designation

In the thirteenth and fourteenth centuries, when the Mongol Empire united vast territories under a single political umbrella, the Church of the East flourished. Mongol khans often patronized Christianity. The patriarch of the church commanded the loyalty of millions of Christians spread across half the known world. Some scholars estimate that at its height, the Church of the East had more metropolitan sees—and thus more ecclesiastical authority—than the Pope of Rome.

Missionary Methods and Adaptation

The Church of the East’s success lay partly in its willingness to adapt to local contexts while preserving apostolic faith. Missionaries learned local languages and incorporated local customs into Christian practice. The liturgy, though always conducted in East Syriac, could be adorned with local musical traditions and artistic styles. The church did not insist on celibacy for all clergy, allowing married men to be ordained as priests and deacons (and, after a brief 5th-century experiment under Barsauma at the Synod of Beth Lapat in 484, reverted to drawing bishops exclusively from celibate monastic ranks)—a practice that facilitated its integration into local communities and the establishment of stable rural clergy.

This adaptability, which would have seemed suspect to medieval Rome, was a strength. It allowed the church to flourish in diverse cultural contexts without sacrificing its apostolic identity.

Catastrophic Decline: Timur and the Ottoman-Safavid World

The Church of the East’s golden age ended abruptly and catastrophically in the late fourteenth century.

The Devastations of Timur

Around 1370, Timur (Tamerlane), the Turco-Mongol conqueror, consolidated power in Transoxiana and launched his campaigns of conquest. Unlike the relatively tolerant Mongol khans, Timur was ferociously destructive. He conquered Persia, Mesopotamia, the Caucasus, and Central Asia, leaving behind a wake of devastation. Christian communities—especially the Church of the East—were decimated. Monasteries were destroyed, bishops were martyred, and entire populations were either killed or displaced.

By Timur’s death in 1405, the Church of the East had suffered irreversible losses. The great monasteries of Central Asia were in ruins. The metropolitan sees of Central Asia and Persia were depopulated. The Indian communities, though isolated, survived. But the grand continental span of the church, its metropolitan sees reaching from the Mediterranean to China, was broken.

Ottoman and Safavid Pressure

The subsequent expansion of the Ottoman Empire (founded c. 1299, with the conquest of Constantinople in 1453 marking its transformation into a Mediterranean superpower) and the rise of the Safavid Persian Empire (1501 onward) further weakened the Church of the East. Both empires were zealously Islamic and actively hostile to Christian minorities. Christian communities were taxed, restricted, and sometimes persecuted.

By the sixteenth century, the Church of the East had shrunk to a small remnant community, concentrated in the mountainous Hakkari region (modern-day southeastern Turkey and northern Iraq), where it sought refuge in inaccessible terrain. The grand metropolitan sees of antiquity were no more. The church had been reduced from a continental power to a persecuted minority.

The Chaldean Catholic Uniate (1552)

In 1552, amid Ottoman pressure and seeking the protection that union with Rome might afford, a portion of the Church of the East under Patriarch John Sulaqa entered into communion with the Roman Catholic Church. This union gave rise to the Chaldean Catholic Church, one of the 23 sui iuris (self-governing) Eastern Catholic churches in full communion with Rome.⁠⁶

The distinction between the Assyrian Church of the East (not in communion with Rome, maintaining apostolic independence) and the Chaldean Catholic Church (in communion with Rome) is crucial. Both trace their ancestry to the ancient Church of the East. Both use the East Syriac liturgy and maintain married clergy (at least for priests; bishops are typically celibate). But the Chaldean Catholic Church recognizes papal primacy and infallibility, submits to Vatican authority, and maintains communion with the worldwide Catholic Church.

The split was driven more by jurisdictional and political pressures than by a Christological dispute, though the Chaldean Church’s subsequent acceptance of papal primacy and (after 1870) infallibility introduced doctrinal commitments the Assyrian Church does not share. (The 1552 election of Sulaqa is the symbolic origin of the Chaldean Catholic Church; the modern unbroken patriarchal line in communion with Rome dates from 1830, when Pope Pius VIII confirmed Yohannan VIII Hormizd as Patriarch of Babylon of the Chaldeans.) Yet it meant that the ancient church’s unity was fractured into two bodies, each claiming legitimacy and apostolic succession.

Theology and Liturgical Life: The East Syriac Tradition

To understand the Church of the East as a living tradition (not merely as a historical curiosity), one must grasp its theological distinctives and its continued liturgical practice.

Christology in East Syriac Vocabulary

The Church of the East, in the classic formulation associated with Babai the Great (d. 628), teaches Christ as one parsopa (person) in two kyane (natures) and two qnome (concrete subsistences or individuated instances of those natures). These terms, rooted in Antiochene theology and perpetuated in East Syriac philosophical tradition, operate somewhat differently from the Greek hypostasis and ousia of Chalcedon. Kyane corresponds roughly to the Greek physis/ousia (nature/essence); qnome functions much like the Greek hypostasis, denoting not merely an abstract universal but a concrete mode of subsistence; and parsopa corresponds to prosopon (person).

In this framework, Christ’s divine kyana (nature) and human kyana (nature) remain truly distinct, each subsisting in its proper qnoma—not confused or fused—yet united in a single parsopa, a single person, a unified face presented to the world.

This is not a heretical compromise between Nestorian dualism and Monophysite fusion. It is, rather, an authentic articulation of two-nature Christology in different conceptual vocabulary. As the 1994 Common Christological Declaration of Pope John Paul II and Mar Dinkha IV affirmed, this confession expresses the same faith in Christ that Chalcedon defended. (The Declaration is a joint ecumenical statement of papal authority rather than an ex cathedra dogmatic definition, but it carries significant magisterial weight for Catholic engagement with East Syriac Christology.)

The Anaphora of Addai and Mari

The Liturgy of Addai and Mari remains the spiritual heart of the Church of the East. This ancient Eucharistic prayer, with core elements dating to at least the third century and continuous use across the East Syriac tradition since at least the seventh, embodies the church’s theology in liturgical form.

The prayer emphasizes Christ’s redemptive work: His Incarnation, His teaching, His passion, resurrection, and ascension. It invokes the Holy Spirit to descend upon the gifts of bread and wine, transforming them into the body and blood of Christ. Uniquely among the great historic anaphoras, the words of institution (“This is my body… this is my blood”) are not recited in a single continuous narrative but are, in the Vatican’s own description, “present… not in a coherent narrative way and ad litteram, but rather in a dispersed euchological way”—woven throughout the prayer itself.

This ancient practice, long questioned by Rome, was formally recognized in 2001 as a legitimate expression of apostolic Christianity. The Vatican concluded that the words of institution are genuinely present and operative in the prayer, even though they are dispersed rather than gathered into a single narrative formula. In this, the Church of the East preserves a very primitive form of Eucharistic theology, predating the later Western emphasis on the institution narrative as a discrete narrative block.

Clerical Marriage and Monasticism

Unlike the Latin Church, which from the twelfth century onward (canonically anchored in the First Lateran Council of 1123 and Second Lateran Council of 1139, building on the eleventh-century Gregorian Reform) required celibacy of all clergy in major orders, the Church of the East permits priests to marry. Bishops are drawn from celibate monastic ranks, but ordinary priests may (and typically do) have wives and children. This practice, rooted in apostolic times and maintained throughout the church’s history, has enabled the church to sustain a living priesthood and to integrate fully into family and community life.

A paradox worth noting: despite the celibate-bishop norm, the Church of the East developed a system of hereditary patriarchal succession from the mid-fifteenth century onward (the Bar-Mama or Shimun line, beginning with Patriarch Shemʿon IV Basidi, d. 1497). The mechanism was uncle-to-nephew: the reigning patriarch, himself a celibate monk, would designate a nephew who would enter monastic life, be consecrated bishop, and eventually succeed his uncle as Catholicos-Patriarch. The office thus stayed within a single family for centuries without violating the celibate-bishop rule. This hereditary system—and the abuses it sometimes produced—was one of the principal grievances that led to the 1552 schism and, later, to the 1968 split of the Ancient Church of the East.

The Church of the East also maintains a monastic tradition of significant scholarly and spiritual importance. Its monasteries have been centers of theological learning, biblical scholarship, and spiritual discipline. The School of Nisibis (5th–7th centuries), the Great Monastery on Mount Izla (founded in 571 by Abraham of Kashkar above the city), and the Monastery of Beth ʿAbe in northern Iraq (founded in 595/6 by Yaʿqub of Lashom) served as the principal places of learning where the church’s theological tradition was developed and preserved. The famous Rabban Hormizd Monastery near Alqosh in northern Iraq (founded c. 640 AD), later the patriarchal residence of the Eliya line, became a great center of manuscript and scribal transmission.

The Biblical Canon and Liturgical Distinction

The Church of the East recognizes a biblical canon distinct from the Western Catholic canon. Its Old Testament, transmitted in the Peshitta, was translated primarily from the Hebrew rather than the Septuagint, and the deuterocanonical books (Tobit, Judith, Wisdom, Sirach, Baruch, 1–2 Maccabees) circulate within the tradition with a variable or subordinate status rather than the full canonical standing they enjoy in the Catholic West. The New Testament canon is also distinctive: the traditional Peshitta New Testament contains only twenty-two books, omitting 2 Peter, 2 John, 3 John, Jude, and Revelation. These five books were translated into Syriac in the later Philoxenian (508 AD, commissioned by the Miaphysite Philoxenus of Mabbug) and Harklean (615/616 AD, by Thomas of Harkel) versions—both produced within the West Syrian / Syriac Orthodox tradition rather than within the Church of the East. Modern printed Bibles used in the Assyrian community (notably the 1979 United Bible Societies edition) generally include all twenty-seven books by drawing on those later Syriac versions, but the five “Western” books have never entered the Church of the East’s lectionary, and the traditional twenty-two-book Peshitta remains the canonical norm of received tradition. (The Chaldean Catholic Church, in full communion with Rome, accepts the full twenty-seven-book Catholic New Testament canon.)

More distinctively, the Church of the East preserves a unique liturgical and spiritual tradition developed over centuries in a non-Western context. Its hymnody and mēmrē (verse homilies)—the great metrical sermons of saints like Ephrem the Syrian, Narsai, and Jacob of Serugh—represent some of Christendom’s most sublime theological and poetic expression.

The Church of the East Today: A Living Witness

The modern heirs of the Church of the East together number roughly one million faithful worldwide: the Assyrian Church of the East with perhaps 300,000 to 500,000 members, the Chaldean Catholic Church with about 600,000, and a smaller body in the Ancient Church of the East. They are concentrated in Iraq, Iran, Syria, and diaspora communities in the West (particularly in the United States and Australia). Together they remain a living, apostolic communion with unbroken succession and a vibrant spiritual life.

The Assyrian Church of the East

The Assyrian Church of the East, not in communion with Rome, is the larger of the two Eastern bodies claiming descent from the ancient Church of the East. Its patriarch is based in Erbil, Iraq (though the See has shifted geographically due to modern conflicts). The church maintains the marks of apostolic life: apostolic succession, the ancient East Syriac liturgy, and what Catholic teaching describes as “true sacraments” preserved through unbroken episcopal succession.⁠⁷ Its own 2001 Holy Synod, following Mar ʿAbdishoʿ of Nisibis (d. 1318) in the Marganitha (“Pearl”), enumerates seven sacraments in an order distinctive to the East Syriac tradition: Priesthood, Holy Baptism, Oil of Unction, the Oblation of the Body and Blood of Christ (Eucharist), Absolution, the Holy Leaven (Malka), and the Sign of the Living Cross.

The Assyrian Church of the East has suffered enormously in the twentieth and twenty-first centuries. The Assyrian genocide that began in 1915—the Sayfo, “the year of the sword,” perpetrated by Ottoman state forces together with allied Kurdish, Chechen, and Circassian irregular and tribal militias against Armenian, Greek, and Assyrian Christians—killed an estimated quarter to one-half of the Assyrian population (roughly 250,000–300,000 dead out of a pre-war population of about 600,000), with the violence extending through 1918 and beyond.⁠⁸ The Simele massacre of August 1933 in Iraq killed between several hundred (British sources) and several thousand (Assyrian community estimates) more.⁠⁹ Most recently, the rise of ISIS in 2014–2017 led to the displacement of more than 120,000 Christians—most of them Assyrian, Chaldean, and Syriac—from their ancient homeland in the Nineveh Plain.

Yet the church persists. Despite trauma, persecution, and diaspora, it maintains its apostolic faith, its ancient liturgy, and its missionary consciousness. The current Patriarch, Mar Awa III (elected in 2021), leads the church in bearing witness to Orthodox Christianity in the Middle East and in supporting diaspora communities worldwide.

The Chaldean Catholic Church

The Chaldean Catholic Church, in full communion with Rome, has similarly endured. It maintains the same apostolic succession, the same East Syriac liturgy, and the same theological tradition as the Assyrian Church. The difference lies in its submission to papal authority and its integration into the worldwide Catholic communion.

The Chaldean Catholic Church also suffered profoundly during the Iraqi wars and the subsequent rise of ISIS. Thousands of Chaldean Catholics fled Iraq. The Patriarch, Louis Raphael I Sako (elected in 2013), has been a prophetic voice for persecuted Christians in the Middle East and a bridge between the Eastern Catholic world and Rome.

The Ancient Church of the East and Reconciliation

A third, smaller body is worth noting: the Ancient Church of the East, which formally separated from the Assyrian Church in 1968 with the election of a rival patriarch, Mar Toma Darmo. The split was triggered by the liturgical and calendar reforms introduced by Patriarch Mar Shimun XXIII in 1964 (including the adoption of the Gregorian calendar), but it was equally driven by long-standing disputes over hereditary patriarchal succession and the patriarch’s prolonged absence from Iraq. In May 2022, representatives of the Assyrian Church of the East and the Ancient Church of the East met at St. Odisho Church in Chicago (and again at Mor Sarkis Church in Skokie, Illinois, on 17 May) and began formal reunification talks, described in press coverage as “a first step on the long and difficult path” toward reconciliation. Full reunion has not yet been achieved, but the two churches are in active dialogue.⁠¹⁰

These talks, though little-noticed in the West, are theologically significant. They represent a movement toward unity among the Eastern churches and a recognition that ancient ecclesial bonds should not be sundered over disciplinary matters.

Ecumenical Recognition and the Common Christological Declaration (1994)

From Polemic to Sister Church

A watershed moment in the Church of the East’s modern history came on November 11, 1994, when Pope John Paul II and Mar Dinkha IV, Patriarch of the Assyrian Church of the East, signed the Common Christological Declaration.

For nearly sixteen centuries, the Church of the East had been labeled “Nestorian,” accused of Christological heresy, and effectively isolated from the broader Christian world. The 1994 declaration reframed that history. It explicitly affirmed that both Rome and the Assyrian Church of the East profess the same faith in Christ—true God and true man—and acknowledged that “the controversies of the past led to anathemas, bearing on persons and on formulas,” which the two churches now consign to the past.

The declaration states: “As heirs and guardians of the faith received from the Apostles as formulated by our common Fathers in the Nicene Creed, we confess one Lord Jesus Christ, the only Son of God.” And further: “Living by this faith and these sacraments, it follows as a consequence that the particular Catholic churches and the particular Assyrian churches can recognize each other as sister Churches.”⁠¹¹ It acknowledged that terminological and traditional differences had historically obscured a fundamental agreement in faith.

This recognition was not merely symbolic. It opened the door to closer communion, though full structural unity remains distant. It validated the Church of the East’s claim to apostolic orthodoxy and signaled to the broader Christian world that this ancient church’s theological voice deserves serious engagement.

The Vatican’s Validation of the Anaphora

In 2001, the Vatican further affirmed the Church of the East’s liturgical tradition by officially recognizing the validity of the Liturgy of Addai and Mari, the ancient Eucharistic prayer that lacks an institution narrative. This recognition, issued by the Pontifical Council for Promoting Christian Unity, acknowledged that consecration can occur through the church’s ancient prayer tradition without the explicit recitation of Christ’s words at the Last Supper.

Significance for Western Christians

Why should Western Christians care about the Church of the East? Several reasons compel attention.

First, the Church of the East testifies to the catholicity of Christianity. The faith Jesus first taught in Aramaic found expression not only in Greek and Latin but also in Syriac. The Christological questions that the councils of Ephesus and Chalcedon wrestled with were not settled in a single moment of perfect clarity; different Christian communities, working in different linguistic and philosophical traditions, developed distinct but fundamentally compatible ways of expressing the same apostolic faith. The Church of the East reminds us that Christianity is larger, more diverse, and more venerable than a merely Western narrative can capture.

Second, the Church of the East provides a living example of apostolic continuity in hostile circumstances. For nearly two thousand years, often under persecution, often isolated from other Christian communities, the Church of the East has maintained unbroken apostolic succession, true sacraments, and faithful transmission of much of the apostolic deposit. From a Catholic standpoint, full visible communion with the successor of Peter remains by divine design the normative form of ecclesial life (so Vatican I and Lumen Gentium 18, with Lumen Gentium 8 on the unique Church of Christ subsisting in the Catholic Church); yet the Church of the East’s persistence—without Christian imperial sanction, without Latin conciliar validation, and largely outside the protection of any Christian state—is a remarkable witness to the resilience of apostolic Christianity in conditions Western Christians scarcely had to imagine until very recently.

Third, the Church of the East’s liturgical and theological tradition enriches the broader Christian world. The Liturgy of Addai and Mari, with its profound theology and ancient form, stands as a witness to a Eucharistic theology that predates medieval Western developments. The church’s Syriac theological and spiritual tradition, preserved in saints like Ephrem the Syrian, Aphrahat the Persian Sage, Narsai, and Jacob of Serugh, offers resources for contemporary spirituality that Western Christianity has largely overlooked. The church’s permission of married clergy is consistent with the wider Catholic tradition that celibacy, though deeply valuable, is a discipline rather than something demanded by the nature of the priesthood itself (so Presbyterorum Ordinis 16).

Fourth, the Church of the East challenges Western triumphalism. For centuries, Western Christianity (both Catholic and Protestant) has operated with the assumption that the great divisions in Christianity are essentially the business of the Western tradition—that Catholicism and Protestantism are the primary players. The Church of the East reminds us that vast Christian populations, with their own apostolic pedigree and theological sophistication, developed and flourished independent of Western ecclesiastical politics. Christianity’s story cannot be told as a Western narrative without serious distortion.

Finally, the Church of the East’s modern witness of persecution and endurance is deeply relevant. In the twenty-first century, when Christian communities in the Middle East face extinction, the witness of the Assyrian Church of the East and the Chaldean Catholic Church—maintaining faith and liturgy in their ancestral lands despite centuries of persecution and recent displacement—is a powerful testimony to the Spirit’s work in history. Western Christians who learn this story are called to deeper solidarity with persecuted Christians everywhere.

The Ongoing Mystery of Two Natures and One Person

At the heart of the Church of the East’s theological witness lies the mystery that occupied the ancient councils: How can Christ truly be God and truly be human? How can the infinite Word become flesh without ceasing to be infinite? How can the eternal God experience time, suffer, and die without compromising His divinity?

The Council of Chalcedon (451) confessed “one and the same Christ, Son, Lord, only-begotten, acknowledged in two natures which undergo no confusion, no change, no division, no separation… coming together to form one person and subsistence.”⁠¹² These adverbial formulas mark the limits of human language when approaching the mystery of the Incarnation. They do not explain the mystery; they protect it from false explanation.

The Church of the East, using Syriac philosophical categories rather than Greek ones, confesses the same mystery. As the 1994 Common Christological Declaration affirms, the two churches share “the same faith in the Son of God,” and the divisions of the past “were due in large part to misunderstandings.” Genuine philosophical complexity remains—Babai the Great’s two-qnome formulation is a substantive Syriac claim, not merely Chalcedon translated—but the shared confession of one Lord Jesus Christ is real.

This realization—that the ancient quarrels were due in large part to linguistic and cultural misunderstanding—ought to humble Western Christian theology. It suggests that doctrinal diversity, grounded in genuine apostolic faith, is not always scandalous division but sometimes the natural flowering of Christianity’s catholicity.

Conclusion: The Forgotten Fourth

The Church of the East stands in Christian history as a monument to apostolic fidelity, missionary courage, and theological sophistication. It reminds us that the splits of 431 and 451 did not merely divide the Christian world into East and West; they created parallel Christianities, each claiming apostolic succession, each preserving true sacraments, each bearing witness to Jesus Christ in its own cultural and linguistic context.

For roughly fourteen centuries—from its apostolic origins to its catastrophic shrinking under Timur in the late fourteenth century—the Church of the East flourished on a scale that dwarfs the imagination of modern Western Christians. Its missionaries traversed the Silk Road. Its patriarchs commanded the loyalty of millions. Its monasteries became seats of learning. Its liturgy, ancient and profound, was prayed in dozens of languages across half the world. And in the diminished but unbroken witness of its modern heirs, the Church endures into its third millennium.

That this great church has become nearly invisible to Western consciousness is a tragedy of historical amnesia.

Yet the church persists. In Iraq, Syria, and diaspora communities worldwide, Assyrian Christians and Chaldean Catholics continue to pray the Liturgy of Addai and Mari, to ordain bishops, to confess the faith of Nicea and Chalcedon (in their own vocabulary), and to bear witness that Christianity is far larger, older, and more diverse than a Western narrative can capture.

The Church of the East is not the “other” Christianity, the heretical rival, the Nestorian sect. It is a sister church, a venerable apostolic communion, a living witness to the universality of Christ’s Body. To encounter the Church of the East is to encounter Christianity as it should be encountered: not as a Western religion, but as a truly catholic faith, spanning cultures and centuries, united in apostolic succession and sacramental grace, bearing the name of Christ across the world.

Western Christians who learn this story are invited to expand their theological and spiritual horizons, to recognize in the Church of the East a voice of authentic apostolic Christianity, and to stand in solidarity with this persecuted but unbroken communion as it navigates the trials of our own age.

Frequently Asked Questions

For Further Study: Commentaries and Sources

• Sebastian Brock and David G. K. Taylor, eds., The Hidden Pearl: The Syrian Orthodox Church and Its Ancient Aramaic Heritage, 3 vols. plus accompanying audio-video volume (Rome: Trans World Film Italia, 2001); individual volumes have been reprinted by Gorgias Press (Piscataway, NJ). A richly illustrated, four-volume reference for the broader Syriac and Aramaic heritage commissioned by the Syriac Orthodox community; especially valuable on the West Syrian (Oriental Orthodox) tradition. Brock is the leading English-language scholar of Syriac Christianity as a whole.
• Christoph Baumer, The Church of the East: An Illustrated History of Assyrian Christianity (London: I.B. Tauris, 2006), provides an accessible, well-illustrated survey of the Church of the East from its origins to the modern period.
• Wilhelm Baum and Dietmar W. Winkler, The Church of the East: A Concise History (London: Routledge, 2003), offers a succinct theological and historical overview.
• Samuel Hugh Moffett, A History of Christianity in Asia, Volume 1: Beginnings to 1500, 2nd rev. ed. (Maryknoll, NY: Orbis Books, 1998), provides extensive coverage of the Church of the East’s missionary expansion across Asia.
• John Meyendorff, Imperial Unity and Christian Divisions: The Church 450–680 A.D. (Crestwood, NY: St. Vladimir’s Seminary Press, 1989), offers the best theological treatment of the fifth-century councils and their context.
• The Liturgy of Addai and Mari is one of the oldest continuously used Eucharistic prayers in Christianity. For scholarly analysis, see Paul F. Bradshaw, The Search for the Origins of Christian Worship: Sources and Methods for the Study of Early Liturgy, 2nd ed. (Oxford: Oxford University Press, 2002), which discusses the anaphora’s primitive character and unique form.
• On the Chaldean Catholic Church and its history, see John Joseph, The Nestorians and Their Muslim Neighbors: A Study of Western Influence on Their Relations (Princeton: Princeton University Press, 1961), which discusses the 1552 union with Rome and the subsequent development of the Chaldean Catholic Church as a sui iuris Eastern Catholic communion.
• On Ephrem the Syrian, the foundational poet-theologian of the Syriac tradition, see Jeffrey Wickes, trans., St. Ephrem the Syrian: The Hymns on Faith, Fathers of the Church 130 (Washington, DC: Catholic University of America Press, 2015); and Sebastian Brock, trans., St. Ephrem the Syrian: Hymns on Paradise, Popular Patristics Series 10 (Crestwood, NY: St. Vladimir’s Seminary Press, 1990). Many works traditionally attributed to Jacob of Nisibis are now identified as belonging to Aphrahat the Persian Sage; the standard term for the great Syriac verse homilies is mēmrā (pl. mēmrē), associated above all with Ephrem, Narsai, and Jacob of Serugh.

Footnotes

1. 1. Pontifical Council for Promoting Christian Unity, “Guidelines for Admission to the Eucharist between the Chaldean Church and the Assyrian Church of the East” (Vatican City, July 20, 2001), published in L’Osservatore Romano. The Vatican concluded that the words of institution are present in the Anaphora of Addai and Mari “not in a coherent narrative way and ad litteram, but rather in a dispersed euchological way,” and that the prayer therefore effects a valid consecration.
2. 2. On the Council of Ephesus (431) and its condemnation of Nestorius, see Norman P. Tanner, ed., Decrees of the Ecumenical Councils, 2 vols. (London: Sheed & Ward; Washington, DC: Georgetown University Press, 1990), 1:37–74. Tanner provides the conciliar documents in both Latin and English.
3. 3. Pope John Paul II and Mar Dinkha IV, Common Christological Declaration between the Catholic Church and the Assyrian Church of the East (Vatican City: Vatican Press, 1994). The declaration is available at https://www.vatican.va/content/john-paul-ii/en/speeches/1994/november/documents/hf_jp-ii_spe_19941111_dichiarazione-cristologica.html.
4. 4. On the “Nestorian” label as a misnomer, see Sebastian Brock, “The ‘Nestorian’ Church: A Lamentable Misnomer,” Bulletin of the John Rylands University Library of Manchester 78, no. 3 (1996): 23–35. Brock argues convincingly that the Church of the East’s theology is not heretical Nestorianism but orthodox dyophysite Christology expressed in different terminology.
5. 5. The Xi’an Stele, erected in 781 AD during the Tang dynasty, records the arrival of the “Luminous Teaching” (Christianity) in Chang’an. The inscription provides valuable evidence of the Church of the East’s presence in China and its theological content as adapted for Chinese audiences. See P. Y. Saeki, The Nestorian Documents and Relics in China, 2nd ed. (Tokyo: Maruzen, 1951), for comprehensive analysis of the Xi’an Stele and other Chinese sources on the Church of the East.
6. 6. The distinction between the Assyrian Church of the East and the Chaldean Catholic Church is primarily jurisdictional rather than Christological, though the Chaldean Catholic Church's acceptance of papal primacy and infallibility introduces doctrinal commitments the Assyrian Church does not share. Both maintain apostolic succession, the East Syriac liturgy, and orthodox faith. See Codex Canonum Ecclesiarum Orientalium (Code of Canon Law for the Eastern Churches) (Vatican City: Libreria Editrice Vaticana, 1990), esp. canons 27–28 (defining sui iuris churches and the five rite traditions); for the current count of twenty-three Eastern Catholic sui iuris churches in full communion with Rome, see the Annuario Pontificio (Vatican City: Libreria Editrice Vaticana, current edition).
7. 7. Catechism of the Catholic Church, 2nd ed. (Vatican City: Libreria Editrice Vaticana, 2000), no. 1399, quoting Unitatis Redintegratio 15: “These [Eastern] Churches, although separated from us, yet possess true sacraments, above all—by apostolic succession—the priesthood and the Eucharist, whereby they are still joined to us in closest intimacy.”
8. 8. On the Assyrian genocide of 1915 and its impact on the Church of the East, see David Gaunt, Massacres, Resistance, Protectors: Muslim-Christian Relations in Eastern Anatolia during World War I (Piscataway, NJ: Gorgias Press, 2006).
9. 9. The Simele massacre of August 1933 in the Kingdom of Iraq, perpetrated under the command of General Bakr Sidqi, killed many Assyrian Christians: official British accounts estimate around 600 killed; Assyrian community estimates run from 3,000 to 6,000. See Khaldun S. Husry, “The Assyrian Affair of 1933 (I)” and “(II),” International Journal of Middle East Studies 5, nos. 2–3 (1974): 161–176 and 344–360; Sargon Donabed, Reforging a Forgotten History: Iraq and the Assyrians in the Twentieth Century (Edinburgh: Edinburgh University Press, 2015).
10. 10. The Ancient Church of the East separated from the Assyrian Church of the East with the election of Mar Toma Darmo as a rival patriarch in 1968, following the calendar and liturgical reforms introduced by Mar Shimun XXIII in 1964 and disputes over hereditary succession and the patriarch’s prolonged absence from Iraq. In May 2022 representatives of both churches met at St. Odisho Church in Chicago and began formal reunification talks, characterized as “a first step on the long and difficult path”; full reunion has not yet been concluded.
11. 11. Common Christological Declaration (1994). The declaration acknowledges that “the controversies of the past led to anathemas, bearing on persons and on formulas” and that “the divisions brought about in this way were due in large part to misunderstandings,” consigning those historic anathemas to the past. No single dramatic ceremonial event of mutual excommunication ever occurred between Rome and the Catholicos of Seleucia-Ctesiphon comparable to the 1054 Rome–Constantinople rupture, since the Church of the East had declared its jurisdictional independence from the Antiochene patriarchate at the Synod of Dadyeshu (424), well outside the Roman imperial system. Nonetheless, layered, asymmetrical mutual anathemas did accumulate over centuries: the Council of Ephesus (431) and the Second Council of Constantinople (553, the Three Chapters) anathematized by name figures the Church of the East venerated (Nestorius, Theodore of Mopsuestia, and the relevant writings of Theodoret and Ibas), while East Syriac liturgical sources (the Ḥudra and the Memorial of the Greek Doctors) preserved anathemas against Cyril of Alexandria. In 1997 the Assyrian Holy Synod under Mar Dinkha IV formally voted to remove from the liturgy all anathemata directed against others.
12. 12. The Council of Chalcedon (451), Definitio Fidei, in Norman P. Tanner, ed., Decrees of the Ecumenical Councils, 1:86–87 (English translation). These four adverbial qualifiers (asynchytōs, atreptōs, adiairetōs, achōristōs) mark the boundary of conciliar language when approaching the mystery of the Incarnation.