POPE BENEDICT XVI will arrive in Mexico on March 23rd to spend three days preaching mainly to the converted. Mexico is one of the world's great Catholic bastions: 83% of its 112m people are loyal to the Vatican, and Mexico City's Basilica of Our Lady of Guadalupe vies with St Peter's in Rome as the world's most-visited Catholic church. The Pope will stay in Guanajuato, Mexico's most devout state, where 94% of the population is Catholic. Well before his visit, posters went up to welcome the pontiff (though many depict his predecessor).
Yet outside the bunting-lined streets of Guanajuato, the Vatican's grip is weakening. The share of Mexicans saying they are Catholic fell by five percentage points in the decade to 2010. In 1970 the figure was 96%. Many of these souls have been claimed by evangelical Christianity, from imported groups such as Baptists, to home-grown sects such as Luz del Mundo (Light of the World). In the south-east Catholics now make up less than two-thirds of the population (see map).