It's 11 am on a Sunday morning, and the mariachi band of Cuernavaca are in full swing. Like mariachi players throughout Mexico they're famed for their romantic serenades, traditionally used by the hombres of Mexico as a way of wooing their mujeres.

But the foot-tapping, trumpet-blasting, violin-strumming sounds being played out here – roof-raising though they are – have nothing to do with lovers, and everything to do with the Sunday liturgy. Because this is 10.30 am Mass in the Cathedral of Cuernavaca – and as usual the church is packed to the rafters, with crowds having flocked from all over Mexico to be part of a religious celebration which incorporates the country's much-loved band sounds.

By the time we get to the sign of peace we're inebriated with jollity, and at least five minutes of hand-shaking and back-clapping ensues before we turn back to the Eucharist.The mariachi players – grey-suited, with flamboyant neck-ties and trousers and jackets emblazoned with shiny buttons – are at the front of the church, and some of the more curious among the congregation are pressing forward to watch them, just as they would if this was a performance in the town square. The hymns are lively and infectious – my Spanish isn't great, and I don't know the words to the songs, but I can't stop myself from humming along and doing a little jive in my pew.

All around me, others are similarly infected by the mood of the moment.  By the time we get to the sign of peace we're inebriated with jollity, and at least five minutes of hand-shaking and back-clapping ensues before we turn back to the Eucharist.

The Mariachi Mass, which has been celebrated here in the Mexican town of Cuernavaca since 1966, was the brainchild of a Canadian priest called Fr Juan Marco Leclerc, who wanted a way of expressing Mexican culture through the Sunday liturgy, and hit on asking a local mariachi group to provide the music. Since then the idea has spiralled beyond his wildest dreams – the Mass, first held weekly in a small chapel in the town, was soon attracting huge crowds and before long it had moved to the Cathedral of the Ascension.  

And now, too, it's spread beyond Cuernavaca – other towns in Mexico have regular Masses with mariachi players, and many churches in the southern states of the US, where there are large Mexican populations, have also followed suit.

What has appealed to all those who have taken up the idea with such gusto is the chance to celebrate Mass with music that fuses the native Indian sounds with the music of Spain. Before the arrival of the Spanish to Mexico, in 1519, the music of the region was dominated by flutes, horns and drums. But with the Spanish came violins and guitars, and more than any other form of music it is the mariachi that combines these two groups of sound. Given that Mexican Catholicism has always been infused with the traditional religions that preceded it here, it seems entirely fitting for the mariachi music to have been incorporated into the Mass.  

Visitors to Cuernavaca who come here for the famous Mass find themselves spoilt for more of interest, because the area groans with fascinating history, not least the history of the cathedral and its founders. Hernán Cortés, the first Spanish leader, was a big fan of the town, and for good reason – it's known throughout South America as the place of eternal spring, with temperatures usually hovering around the mid-20s centigrade, and the blossoms seemingly always in bloom. Cortés built a palace here, which today is packed with colonial art and weaponry – and much later, in the twentieth century, the muralist Diego Rivera, husband of Frida Kahlo, came here to paint a series of murals depicting the history of Mexico around the palace’s courtyard.

Unsurprisingly, given its popularity with Cortés, the Franciscans decided to found one of their first churches in the Americas in Cuernavaca. Their original site of worship was an open-air church, which can be seen in the town to this day.

Cortés, mindful of the benefits of building an impressive new church in the midst of his favourite part of Mexico, soon weighed in with an enormous cathedral. And a multi-purpose cathedral at that – in case of trouble, Cortés had the cathedral designed as a fortress, and had cannons mounted on the buttresses.
It all combines to make a trip to the extensive cathedral complex a fascinating experience. Come on a Sunday for the Mariachi Mass and you'll find plenty to entertain you for the rest of the day on the cathedral’s large and leafy compound itself. What’s fascinating about the main cathedral building, apart from its extraordinary fortress-like exterior, is that inside it’s almost bare –and given that Catholic churches in Mexico tend to be festooned with gold and gilt and packed with art and statues, that makes it extremely unusual. The altar is stripped and plain, with just a large canopy above, and the only adornments are large quotes from Scripture (‘El que me come vivira’ – ‘Whoever eats me will have life’).  

But there is one huge, and extraordinary, piece of art here, and it takes up most of one entire wall of the vast cathedral building. It’s a mural, painted in an Asian style, and it tells the story of St Philip of Jesus, who was born in Mexico City to a Spanish family in 1572. Philip was apparently a frivolous young man but he nonetheless decided to become a Franciscan; however, he didn’t last long in the novitiate and left to pursue a career in business. Within a few years, though, he was back as a Franciscan, and this time he stuck with it and was ordained.

Fr Juan Marco Leclerc, who wanted a way of expressing Mexican culture through the Sunday liturgy, and hit on asking a local mariachi group to provide the music.At the time Cuernavaca was a staging-post for missionaries en route to Asia, and in spring 1596 Philip came here on his way across Mexico to the port of Acapulco, from where he was due to sail, with a group of fellow Franciscans, to the Philippines. They set out in July, but the voyage went badly wrong and they were shipwrecked on the coast of Japan. The local governor, believing that they were an advance party of invaders, had them locked up – and later, when they were allowed to go to a monastery, they were held under house arrest.  

But things went from bad to worse: early the following year the group was moved by the Japanese authorities to Kyoto, where they had their ears cut off and were paraded through the streets. They were then taken to Osaka en route for Nagasaki, where they were finally crucified on a hillside – more than twenty in all, including the 25-year-old Philip, who was canonized in 1862 by Pope Pius IX – Mexico’s first saint, who was later made the patron saint of Mexico City.

The murals on the wall at Cuernavaca trace the story of the journey of Philip and his companions in their ship, and then their martyrdom in Japan. The row of crucifixes, even today, is a shocking sight – and though the paintings (which were only discovered by chance a few years ago during redecorations) are faded, the story they depict is clearly told.
As well as the main cathedral building, the compound boasts several other chapels of which the most splendid is the Capilla del Santisimo, which has a gilt altarpiece and the Stations of the Cross done in charcoal on paper.  

And before you go, head down to the crypt chapel where there’s a memorial to Bishop Luis Cervantes, one of the country’s best-known clerics until his death in 2000. It was under his prelature that the Mariachi Mass was instigated here – so it’s thanks to him that the 10.30 am Mass each Sunday goes with such a swing, and pulls in so many crowds.