360th anniversary of Coonan Cross Oath (Koonan Kurishu Satyam).
The Roman Catholic faith started to had its foothold in Malankara with the arrival of Vasco De Gama, the famous Portuguese sailor in 1498. Initially the Portuguese Priests concentrated on the poor people living on the sea coast of Kerala and Goa and converted many to the Latin Catholic faith, some times even forcibly. But later they tried to introduce their faith among the Syrian Christians... of Kerala. For that they even adopted some unholy practices.
On June 20, 1599 the Roman Catholic Archbishop Menezes, with the help of local rulers, convened the historical Synod of Diamper (Udayamperoor) and thereafter started forcibly converting the Syrian churches as Latin, burned all the historical documents, and thereby terrified the Syrian Christians. The Malankara Church had to suffer servitude and indignities under the Roman Catholic bishops.
Finally in response to the continuous appeal of the Thomas Arkadiyakon (archdeacon), who was then giving leadership to Malankara Church; from the Patriarchate of Antioch came Mor Ignatius Ahattula in 1653. The tradition is that the Portuguese arrested him, tied him up and cast him in the Ocean. Consequently, the Syrian Christians get agitated and as a result, a large gathering of about 25,000 assembled at Mattancherry and took Oath at 'Koonan Cross' which happens to be known as the historical 'Koonam Kurisu Sathayam' in 1653 and declared that they and their future generations will ever be loyal to the throne of Antioch and also vowed to fight against the atrocities of the Roman/Latin Catholics.
The Malankara Church sent request to the Patriarch of Antioch again and in 1665 Saint Gregorios of Jerusalem was deputed to Malankara. The link between Malankara and Antioch that was broken and remained separated for about 150 years was re-established with the arrival of this holy father. Saint Gregorios ordained, Arakadiyakon as Bishop who assumed charge as MarThoma I. And once again, Malankara Church become the integral part of the Syrian Orthodox Church, adopting its rituals, rites and liturgy as before.