By Mark Duff BBC religious affairs reporter

Mexico's first indigenous saint, Juan Diego, is said to have had a vision of the Virgin Mary almost five centuries ago.

Some of the images of Juan Diego show him every inch the conquering Spaniard rather than the native Mexican

Juan Diego is the focus of intense devotion in Mexico.

The story of a humble peasant's vision of the Madonna still has immense power in a country where religious symbols carry a powerful emotional charge in ordinary people's lives.

Pilgrims flock to the Basilica which was built on the site of his reported vision of a dark-skinned Virgin Mary in December 1531.

But at this point certainty starts to fade.

'Convenient tool'

According to the Vatican, both the vision and Juan Diego's death were well-documented - and the Virgin left an image of herself imprinted on his cloak.

Pilgrims gathered to welcome the Pope to Mexico

According to critics, the whole story is a pious fiction - and Juan Diego never existed.

According to this theory, he was a convenient tool in the Spanish battle to win over indigenous Indians to Catholicism, by fair means or foul.

Some will view the canonisation of Juan Diego in the same light - as part of the Catholic Church's counter-attack against the inroads made by Protestant evangelicals over the past couple of decades, especially among native Mexican Indians.

'Symbolic truth'

Catholic historians who question the veracity of the story point to the fact that more than a hundred years passed before it was written down.

Others though, while sceptical about the facts, maintain that the story has a kind of symbolic truth and it should be valued as such - as a kind of parable.

But the controversy doesn't end there.

Some of the images of Juan Diego on sale in Mexico show him as bearded, tall, thin - and pale-skinned: every inch the conquering Spaniard rather than the native Mexican.