Two thousand years ago, St Thomas stopped doubting, trekkking instead to Asia to spread the gospel. He left a trail of holy clues behind him...
A passage to India - that's what you get for being doubtful. Having crushed his uncertainties by touching Christ's wounds, St Thomas set out to evangelise. And, around AD52, he arrived on the west coast of the sub- continent to spread the Word.

At the time, there was already plenty of commerce across the Arabian Sea between the Middle East and India. The main port on the Malabar Coast - and the one where Thomas landed - was Kudangallor. It is now submerged beneath the silt of two millennia.

But just along the coast, in the profoundly colonial city of Cochin, stands the first church to be built by Europeans in India. You would imagine they would naturally bestow Thomas' name upon it. But instead they called it St Francis, because they were a little miffed that Thomas got there before them. You can imagine the entertaining scene in 1498 when the Portuguese arrived.

Using evangelism to justify expansionist conquests, Vasco da Gama must have been crestfallen to find that Christianity was alive and well and living in India, and that he was nearly 1,500 years late. In 1503, the church was built on what is now Fort Cochin. The initial wooden version was replaced within a century by the present stone structure. Later, the church was requisitioned by the Anglicans following Britain's takeover of India. But at least one facet of the original has survived: the tomb of the Portuguese navigator.

Vasco da Gama died in Cochin in 1524 and his remains were interred here for 14 years before being moved back to Lisbon. Despite St Thomas being written out of the local story, those on his trail should start in Cochin, not least because it forms a great introduction to the religious and cultural multiplicity of India.

Here is a Hindu shrine within a Portuguese-Dutch palace; an array of Chinese fishing nets that hang like giant bats' wings, waiting to dip down and sweep up the day's catch; and a beautiful, atmospheric synagogue.

There is still a tiny community of Jews in Cochin, whose place of worship boasts a floor of exquisite Chinese tiles and an air of quiet dignity. The Jewish community in Cochin is thought to have reached India from Palestine even ahead of St Thomas. They, and he, were followed to the sub-continent by a community of Syrian Orthodox Christians, who settled south of Cochin in the town of Kottayam. Fragments of their community remain, but the main reason most tourists come here is for a serene cruise through the backwaters of Kerala. Invest 12 rupees - about 15 pence - and you can spend three hours on a ferry that wafts through a landscape rather like the Norfolk Broads, but with elephants and rice fields.

It may seem inappropriate to reduce the New Testament to the level of English football, but it helps explain my interest in St Thomas. The Carling Premier League saints - gospel-writing Matthews, Marks, Lukes, Johns, plus gifted paragons like Peter, Paul and Patrick - lord it over a whole raft of Nationwide League-level martyrs. As in football, so in religion; this latter group, with notables like Christopher, Michael and Swithin, tends to be much more interesting. And most fascinating of all, the original globetrotting apostle: St Thomas Didymus. Twenty years after the crucifixion, he spread the gospels into Asia.

From the west coast of India, it is thought he evangelised his way across the southern tip of the sub-continent. He eventually reached the Bay of Bengal at present-day Chennai - the city formerly known as Madras - around AD58.

Even today, the journey is a tricky 500 miles across the high Western Ghats, on railways that would challenge the average tank engine. But the diligent seeker after Thomas will take a short diversion north to the museum in Old Goa. This Portuguese colony endured much longer than Cochin - it was surrendered by Lisbon only in 1961. During their rule, the colonials dismantled the original capital, stone by stone, to create the present city, Panjim. But the demolition squads left the religious buildings in a city that looks as though it has been hit by a holy neutron bomb - only the religious buildings survive. In the cloisters adjoining the church of St Francis, sandwiched between an Islamic inscription and a Hindu hero, you discover a small shrine dating from 1630. "This pillar", reads the inscription, "was brought from San Thome, Madras. A piece of the iron of the lance with which St Thomas the Apostle was supposed to have been killed was preserved in the small niche at the top of the pillar." It was natural that the Portuguese would bring some token back from the place of Thomas' death to the archbishopric for the entire sub-continent, Old Goa.

No metal remains, but the detour is rewarding for the glimpses of a once- great city now melting back into the encroaching jungle.

Across in Chennai, the city has well and truly encroached upon the place where Thomas is thought to have preached and been martyred in AD72. Prior to this, it is said that he sailed to China, but failed to make inroads and returned across the Bay of Bengal. Deep in the suburbs, the Church of Our Lady of Health is a neat, prim place that conceals a cave. It was here that Thomas lived, while he conducted worship at the fine beach two miles east.

You can tell you are getting close to the correct location, because extravagant tableaux of Christ and miscellaneous apostles punctuate a horizon that would otherwise be full of the billboards and smog that characterise many Indian cities.

In return for a decent donation to church funds, a gregarious old man - appropriately named Joseph - will guide you around the grotto and explain the significance of the rock where the saint prayed (evident, he says, from what appear to be a pair of paw marks gouged out of it); the miraculous opening that allowed him to escape when troops sent by the local rajah cornered him; and the footprint, now the size of an elephant's hoof, branded onto the rock from which he took his single bound to freedom.

Close by, on a hill close to the present-day airport, he was finally captured and killed with that evil lance - though at least one account maintains his death was an accident caused by a huntsman's stray arrow.

His remains are said still to be in the city, in a crypt just below the altar of San Thome Cathedral - a fine, airy church that provides welcome sanctuary from the fervent city outside. You descend to find a glass case, lit by a single fluorescent tube, and peer vainly into the gloom. At this point you may recall that a town in Italy, Ortona, also claims to possess his relics. It might all be true, but I have my doubts.

Getting there: Simon Calder flew into Chennai (Madras) and out of Mumbai (Bombay) as part of a BA/Qantas return trip to Australia, costing pounds 967 through Quest Worldwide (0181-547 3322).

Accommodation: he paid pounds 1.10 for a night at the Hotel Dhanamani in Madurai; pounds 3 for a night at the Hotel Seaweed in Kovalam; pounds 5 for a night at the Coco Banana Bungalows in Calagute; and pounds 10 for a night at the Chateau Windsor, Mumbai.

Visas: British passport holders require a visa to visit India. For advice, call the 24-hour visa information service (0891 880800) or you can apply in person or by post to any of the following: the High Commission of India, India House, Aldwych, London WC2B 4NA; or Consulate-General of India, The Spencers, 19 Augustus Street, Jewellery Quarter, Hockley, Birmingham B186DS; or the Consulate-General of India, Fleming House, 134 Renfrew Street, Glasgow G3 7ST.

If applying by post, first send a stamped addressed envelope for a visa application form to the Postal Visa Section at either address above. Postal applications take up to four weeks. Once completed, send the form with two passport photos, your passport, and the fee of pounds 19. "You are advised not to finalise your travel arrangements until your visa has been issued," says the High Commission