Christianity: Trade between India and West Asia since ancient times was not only feasible, but common, and ports in the Western sea coast state of Kerela were well visited by such travelers. St. Thomas the Apostle arrived in Kodungalloor in Kerala on Nov. 21(?) 52 AD, and attempted to preach the Gospel to the Jews settled there. However, he was more successful in preaching to the Keralites and baptizing a number of high caste Hindus, including members from royal families, who formed the first Christian community in India. He then moved on to other kingdoms, probably reaching Sri Lanka, and returning to Madras in 72 AD where he was martyred that year. Indeed, the early Christians of India were known as Thomas Christians - until the advent of the Portuguese in the 16th century followed closely by the British.
The arrival of St. Thomas was recognized by several writers from west Asia since 2nd century. The doctrine of the Apostle Thomas and the Acta Thomae, both of which are written at or near Edessa, circa 200-250 AD. St. Ephrem, St. John Chrisostom and St. Gregorios Nazianzen, in the 4th century, St. Jerome circa 400 AD, historian Eusabius circa 338 and Theodore of the 5th century attest to Apostle Thomas in India. History has it that His Grace Mar John, Archbishop of India, represented the Indian church in the Council of Nicea, in the year 325. In his signature to the decrees of the Council, he gives his title as "Prelate of Metropolitan of Persia and the Bishop of Great India". These Christians in India had no written records but an oral tradition handed down by their elders and to these they were most tenaciously attached. They lived under native princes who rarely interfered with their faith and one of the paramount Rajahs of Malabar, Cheruman Perumal, had conferred on them a special civilian status. Thus these Christians obtained status above the lower classes, and made them equal to the middle class in the country. The honorific appellation bestowed upon them by the rulers of the country is that of "Mapla", which signifies great son or great child, and they are commonly called ‘Mapla’ by the people even to this day. However, these St. Thomas Christians now prefer to be called the Nasrani (Nazarenes), the designation given by the Mohammedans to all Christians.
Today, 2.5% of India's population are Christians, and Christianity is the third most populace religion in India.