Christianity in India is as old as Saint Thomas, one of the Apostles of Jesus Christ. He is believed to have landed some where near Cochin in Kerala, by the middle of the first century AD. After having preached the Gospel and having founded several Christian communities, he went to Madras because of local antagonism to his religious activities. St. Thomas was finally killed there, by some of his opponents.
Other legends describe Saint Bartholomew as the first Christian missionary in India. Christian missionary activity can be said to have begun with the arrival of Saint Francis Xavier in 1542. Saint Francis Xavier was succeeded by Portuguese missionaries.
Until The sixteenth century the Christians of Saint Thomas formed a stable and well organized church. By about 1500 AD they were founded only in the central regions of modern Kerala, but later existed in many more places. The declining state of affairs among the St. Thomas Christians were due to the repeated invasions that affected nearly the whole of India.
The St. Thomas Christians belong to a section of Christianity, which is called as the Eastern church. There are several Christian communities with the same Eastern tradition. St. Thomas Christians lost their primeval unity and got divided. The majority is united with the Pope, regarded by Catholics as the supreme leader, keeping their autonomy and originality. Those St. Thomas Christians who are living more on their own are called either orthodox or Mar-Thomites, or simply Christians of the East.