DOES IT REQUIRE a catastrophe such as war or a pandemic to make Christians see their commonalities and break bread together?

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The unified Catholic/Orthodox Liturgy celebrated jointly between the Byzantine Orthodox and the Latin clergy was a modified version of the Divine Liturgy of Saint John Chrysostom. It which mentions the name of the Pope and recited the doctrinal decrees of the Council of Ferrara-Florence (the 1438-45 council in Rome in which the Latin and Greek churches had tried to reach agreement on their doctrinal differences and end their schism).

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Meanwhile the Muslim invaders of Sultan Mehmed II’s military were firing canons at the city and the men of the Ottoman Empire were throwing ropes over the walls.

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There were indeed several formal joint Catholic and Orthodox masses and reconciliation efforts prior to May 1453. It would be cynical to presume that these celebrations did not spring from a mutual yearning for organic theological harmony, and not as if they were mere politically desperate attempts by the Byzantine Empire to secure Western military aid against expanding Turkish forces. Indeed, they are remarkable events in church history. But they could have happened regularly and taken root throughout all of Christendom.

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Thus, important concordats, those sadly never happening, represented inter-ecclesiological failures except for the final one, which presents a warning to us. That joint Liturgy and Communion needed to happen literally at gunpoint, because its occurrence was dependent on the irony that only looming tragedy could force Christians into unity with one another.

Below are the attempts, with only the final try succeeding, but requiring a Christian empire to die:

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The Council of Lyon (1274): Byzantine Emperor Michael VIII Palaiologos sought an alliance with Pope Gregory X to stop Western crusaders from attacking his empire. An embassy was sent to Lyon, and a formal union was read at Hagia Sophia, though it was deeply despised by the Orthodox public and collapsed as soon as the political threat shifted.

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The Council of Florence (1438–1445): Emperor John VIII Palaiologos and Patriarch Joseph II of Constantinople traveled to Italy to negotiate military aid. A decree of union, Laetentur Caeli, was signed on July 6, 1439, by representatives of both East and West.

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The Official Union Proclamation at Hagia Sophia (December 12, 1452): Because the Ottoman siege was imminent, the decree signed at Florence was finally implemented in Constantinople. Papal legate Cardinal Isidore of Kiev celebrated a formal, joint Catholic-Orthodox Divine Liturgy inside Hagia Sophia. However, it proved deeply controversial—many Orthodox clergy and citizens boycotted the service, famously declaring they would “better the turban than the tiara.”

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The Latin Empire (1204–1261): Following the catastrophic Fourth Crusade, Western Crusaders seized Constantinople and converted Hagia Sophia into a Roman Catholic cathedral. While this period was marked by forcible Latinization and not a voluntary joint effort, Catholic masses were actively held there.

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Despite these prior milestones, the unions never took root in the hearts of the Greek faithful. The final joint liturgy held on May 28, 1453, during the active siege, saw Greeks and Latins praying side-by-side on the same battlements and partaking in sacraments together under the dome. Albeit united ostensibly by their impending doom, their desire to share Communion was nonetheless a sincere true ecclesiastical-ecumenical concordat.

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The primary source of the famous final Mass (or Divine Liturgy) held at Hagia Sophia on the night of May 28, 1453—where Emperor Constantine XI and the doomed defenders took communion together—comes mainly from the accounts of George Sphrantzes and The Chronicle of Doukas.

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The specific authors, book titles, chapters, and approximate writing dates for all five sources are detailed below:

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1. George Sphrantzes

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Book Title: Chronicon Minus (Smaller Chronicle) and Chronicon Maius (Larger Chronicle).

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Location: Book 3 (in the Maius) or Section 34 (in the Minus).

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Details: Sphrantzes, a close confidant and diplomat to the Emperor, authored two versions of his chronicle. In Book III of the Chronicon Maius, he briefly recounts the events inside the city before the final assault, the Emperor’s last ride along the walls to inspect defenses, and their emotional farewell.

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Writing Date: The Minus was drafted shortly after his release from captivity in the mid-1450s, while the Maius (which features the most dramatic recounting of the final Mass) was rewritten later, during his retirement in Corfu, between 1467 and 1477.

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2. The Chronicle of Doukas

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Book Title: Historia Turcobyzantina (History of the Byzantines).

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Location: Chapter 37.

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Details: The historian Doukas provides a detailed, dramatic account of the final days of the city. In these chapters, he records the united liturgy and details how the despairing citizens and defenders flocked to Hagia Sophia to pray for salvation before the final breach.

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Writing Date: Composed in the years following the fall of the city, likely between 1455 and 1462.

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3. History of Laonikos Chalkokondyles

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Book Title: Historiarum Demonstrationes (Demonstrations of History).

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Location: Book 8.

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Details: Chalkokondyles details the fall of the city. Though he focuses heavily on political and military aspects, his work remains a primary text detailing the overarching tragedy and final moments leading up to the breach.

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Writing Date: Composed over many years in the mid-15th century, with work extending until roughly 1480.

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4. Letters of Cardinal Isidore

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Book Title: Letters on the Fall of Constantinople (primarily his letter to Cardinal Dominico Capranica, which describes the final liturgy and its immediate aftermath).

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Chapter: No discrete chapter system; the citation is generally identified as his personal correspondence.

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Details: Cardinal Isidore of Kyiv was present at Hagia Sophia as the chief papal representative. In his personal letters written after the fall (specifically in July 1453 from Crete), Isidore provides an eyewitness account of the united service in Hagia Sophia, noting that Greeks and Latins partook of the holy mysteries together in a final act of unity.

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Writing Date: Written in May-July 1453 shortly after his escape to Venetian Crete.

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5. Michael Critobulus

Book Title: History of Mehmed the Conqueror.

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Location: Book 1 (specifically Chapters 60-61).

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Details: A Greek statesman who later served the Ottomon Empire. Cristobulus documents the events directly leading to the capture of the city. He offers a contemporary perspective of the mindset of the defenders, their desperate acts of prayer, and the fall of the city.

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Writing Date: Written in the early 1460s, completed around 1467.

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