Hagios Petros), was the cathedral church of Antioch to the Melkite and Latin patriarch during late antiquity and the Middle Ages.

According to the famous Christian Arab Ibn Butlan, the church was the house of a man called Cassianus, a prince of Antioch, whose son the apostle Peter had resurrected.

The Syrian chronicler John Malalas recounts that emperor Justinian donated a jewelled toga to the inhabitants of Antioch which was then displayed in the church of St Cassian.

The church of Cassian, now referred to as Hagios Petros (i.e. St. Peter), was also reconstructed after the Hagia Sophia by Patriarch John III Polites who was ordered to do so by Emperor Basil II.

[13] The papal legate Adhemar of Le Puy, spiritual leader of the crusaders, was buried in the church upon his death in August 1098.

[20] Ibn Butlan wrote that the church held a relic of John the Baptist (the right hand and possibly arm) which was then smuggled to Chalcedon by Patriarch Hiob and then in 957 to the palace of Constantine VII in Constantinople.

[2] According to the 17th century traveller Jean de la Roque the Christians of Antioch were still able to see the ruins of the church of Cassian though he thought them to be those of the Domus Aurea.

[22] According to Ottoman sources and local traditions, the present-day mosque of Habib Neccar was known in the crusader period as "El Kosyan" (Kasyana) church.

[4] However, this identification conflicts with records of Yaqut al-Rumi who mentions a distinct shrine of Habib as a place of Muslim pilgrimage at the beginning of the thirteenth century when Antioch was under Frankish rule.