The Coonan Cross Oath and a Fractured Inheritance

For roughly a millennium the Saint Thomas Christians were governed by bishops sent from the East Syriac Church of the East, worshipped in Syriac, and operated with substantial local autonomy under a hereditary archdeacon who handled everyday communal leadership. Portuguese colonization of the Malabar coast from 1498 brought this arrangement into direct conflict with Latin Catholic missionaries, who regarded the community's East Syriac connections and married clergy with suspicion. The 1599 Synod of Diamper, convened under Portuguese and Jesuit pressure, attempted to bring the community fully under Latin Catholic norms, revising its liturgy and severing its ties to the Church of the East.

Resentment at this imposition culminated in 1653 in the Coonan Cross Oath, when a large part of the community gathered at a leaning stone cross in Kerala and swore never again to submit to Portuguese Jesuit authority, a decisive break that set the community's later fragmentation in motion. Over the following centuries, further splits produced the several distinct churches that carry the Saint Thomas Christian inheritance today: Catholic communities in union with Rome under Eastern rites, the Malankara Orthodox and Jacobite Syrian churches connected to Oriental Orthodoxy, and the Reformed-influenced Mar Thoma Syrian Church, all still claiming descent from the same first century foundation despite centuries of division.