It is difficult to comment on the advent of Christianity in India with accuracy due to the lack of any direct evidence. The most accepted and persistent theory associated with the coming of the Christians in India dates back to 52 CE when St. Thomas, one of the 12 apostles of Jesus, had sailed to Muziris (Kerala) with the mission to proliferate Christianity in the lands of the “heathens”. The arrival of the apostle, the patron saint of India, has been corroborated by the hagiologies and liturgies and also by the Syrian Christians themselves. Later some significant medieval treatises such as the one by the Venetian traveller, Marco Polo too picked up this tradition which speaks of the evangelical process in the Malabar region by St. Thomas, proselytizing a number of inhabitants there.
The 1st c. CE was also an era which witnessed active commercial relations between the Mediterranean regions and South India. This, in turn, led to the early migrations of the Jews and Christian communities to Malabar. Besides the merchants coming and settling down in the Malabar coastal areas, there were also refugees who were facing persecutions in their respective native places and had migrated to the tract. However, the commercial interaction between Rome and South India in the early centuries of the Common Era did not seem to contribute much to the propagation of Christianity in the peninsular India in the next few centuries. In the 7th c. i.e. in about 658 CE the churches in South India were in a dilapidated condition. Much later in the late 13th c. an Italian traveller and missionary named John of Monte Corvino is said to have travelled to the Malabar coast and he observed that the number of Christians in the region were not many on account of their persecution.
A new dawn was seen in the history of the Christians in south India when in 1498 a Portuguese explorer, Vasco da Gama was successful in finding an alternative trade route to India via Cape of Good Hope. Earlier the Ottoman Turks in 1453 captured Constantinople (Istanbul) and completely established their monopoly over trade in spices and other oriental goods by controlling trade routes in the Mediterranean Sea and the Red Sea. The loss of Constantinople proved unfavourable to the traders and merchants of Europe. European nations particularly Portugal and Spain were keen on finding a new trade route linking Europe to India. The sovereigns of these countries extended their patronage to the sea voyagers and also to the pirates. It was in this critical state of affairs that in 1498 Vasco da Gama reached Calicut (Kerala). The Arab merchants who were already stationed at Calicut showed hostility to the arrival of the Portuguese sailor. However, zamorin, the local ruler saw a trading opportunity and benefits in dealing with Vasco da Gama and therefore, he was received with open arms. The expedition to Calicut proved to be exceedingly profitable for Vasco da Gama since he received 60 times the profit of the entire voyage. But the expedition was not only significant for the riches it brought along with it but also it inaugurated the coming of the Europeans, an age of colonialism, and the vigorous propagation of Christianity in the Indian subcontinent as well as beyond it. Vasco da Gama on his second voyage to the Malabar Coast in 1502 provided protection to the Christian populace.
In the beginning of the sixteenth century, the Portuguese were able to establish their naval supremacy in the Indian Ocean and the Arabian Sea. Francisco de Almeida, the first Portuguese governor in India fought two consequential naval battles, viz., the Battle of Chaul (1508) and the Battle of Diu (1509) respectively. In the former battle, Almeida fought against a naval alliance formed by the Turks, Arabs, and the Sultan of Gujarat. The Portuguese governor lost the battle as well as his son, Don Almeida. In the next battle in 1509, he defeated the triple naval alliance and thus, laid the foundation of the Portuguese dominance in the Indian Ocean for the next 100 years. The succeeding Portuguese governor, Alfonso de Albuquerque embarked upon a policy which not only advocated the Portuguese supremacy at sea but it also strived to establish dominance over land. Accordingly, forts were set up at many strategic sites and a strong naval force was deployed to safeguard the forts. He expanded the Portuguese territories in India by conquering a critical natural harbour and port called Goa from the Adil Shahi dynasty of Bijapur (1490-1686). All these political actions paved the way for the further propagation of Christianity in South India. At Quilon (Kollam, Kerala) Albuquerque procured certain privileges for the native Christians from its ruler. Missionaries became more active in spreading the gospel.
St. Francis Xavier of the Jesuit Order arrived at Goa in 1542 and was instrumental in converting many natives in the South-East Coast along with Travancore. He is credited to have built 45 churches in Travancore. In his missionary work, sometimes he received hostile treatments such as the ones from the Vijaynagar rulers and at other times, he was accorded royal patronage from the Araviti rulers. His relics are preserved in the Basilica of Bom Jesus in Goa which is now a UNESCO World Heritage Site. Robert de Nobili, Fr. Emmanuel Martin, etc. were other notable missionaries who contributed to the propagation of Christianity in South India.