The Coonan Cross Oath (), also known as the Great Oath of Bent Cross, the Leaning Cross Oath or the Oath of the Slanting Cross, taken on 3 January 1653 in Mattancherry, was a public avowal by members of the Saint Thomas Christians of the Malabar region in India, that they would not submit to the Jesuits and Latin Catholic hierarchy, nor accept Portuguese dominance () in ecclesiastical and secular life. There are various versions about the oath's wording, one version being that the oath was directed against the Portuguese, another that it was directed against Jesuits, and yet another version that it was directed against the authority of Catholic Church. Saint Thomas Christians were originally in communion with the Church of the East, which practiced East Syriac Rite liturgy. However, the Portuguese did not accept the legitimacy of local ecclesiastical traditions, and they began to impose Latin usages upon the local Christians. At the Synod of Diamper in 1599, presided over by Aleixo de Menezes, the appointed Latin Catholic Archbishop of Goa and the Primate of the East Indies, a number of such latinisations were imposed, including the preference for Portuguese bishops, changes in the liturgy, the use of Roman vestments, the requirement of clerical celibacy, and the setting up of the Portuguese Inquisition in Goa and Bombay-Bassein which exercised ecclesial jurisdiction in Portuguese Cochin. In 1653, after half a century of the increasing influence of the Latin Church, the majority of the Saint Thomas Christians resisted Jesuits, and took the Coonan Cross Oath (1653) at Mattancherry, pledging to liberate themselves from latinisation and Portuguese domination. They elected Thoma I as the archdeacon and head of their community and decided to re-establish intercommunion with older Eastern Churches. Background It is believed that the Saint Thomas Christians of Malabar was in communion with the Church of the East from 300 to 1599. Saint Thomas Christians looked to Catholicos-Patriarch of the Church of the East for ecclesiastical authority. Although the bishops from the Middle East were the spiritual rulers of the Church, the general administration of the Church of Kerala was governed by the indigenous Archdeacon. The Archdeacon was the head of Saint Thomas Christians. Even when there were more than one foreign bishop, there was only one Archdeacon for the entire Saint Thomas Christian community. However, with the establishment of Portuguese power in parts of India, the clergy of that