Saint Thomas Christians
A body of Christians in India who claim spiritual descent from the Apostle Saint Thomas, Bishop of Mylapore, who was martyred in 68, according to strong local tradition and collateral evidence.
Various witnesses have recorded that from earliest times a body of Christians dwelt in India and its environs, and, though Saint Thomas is for the first time mentioned in documents c.550, it is highly probable that he was their spiritual father.
Little is known of their first prelates; John the Persian called himself bishop of all churches in Persia and Great India at the Council of Nice in 325, but there is no evidence that he ever visited India.
Up to 496 it is certain that all the bishops were Catholic; from then the prelates came from Babylon, but for a long time the Thomas Christians were deprived of bishops, and when finally that patriarchate sent them priests and prelates, these must have been Nestorians, whom the people, in their anxiety for a hierarchy, unquestionably accepted, doubtless unaware that the Nestorian heresy existed.
When the Portuguese missionaries arrived in 1500 they considered the Saint Thomas Christians Nestorians (despite protestations to the contrary not voiced until three centuries later), and, laboring to reclaim them, a Synod was held in 1599, at Dampier (Udiamparur), where Saint Thomas priests and laymen promised submission to Rome.
But in 1653, schism once more tore them away, only 400 of 200,000 remaining faithful.
These were for the most part retrieved by the Carmelties sent from Rome in 1657 for that purpose.
New Catholic Dictionary