Rome Has nearly 1000 churches.
Yet in the run-up to the millennium Pope John Paul II commissioned a further 50 to serve the city's suburbs. The last of these, la Chiesa del Dio Padre Misericordioso, known simply as the Jubilee Church, was inaugurated in October on the pontiff's 25th anniversary. It is the first Roman Catholic church to be designed by a Jewish architect.

Some of the biggest names in contemporary architecture – such as Frank Gehry, Santiago Calatrava and Richard Meier – were invited to compete for the design. The winner was Meier.

So how did this architect, who had never designed a church before, go about trying to create a contemporary sacred space? "I thought, 'How does one define it and what are the forms that are going to express the difference between the sacred and the secular?', he says. "I felt circular geometry was one way of doing that, as opposed to the rectilinear geometry of the secular spaces."

Three arcing walls sweep along the southern side of the church. Their curves are cut short, but they hint at a trinity of concentric spheres that would otherwise wrap around the building. These shells are wonderfully modern forms but use a symbolic geometry common to Renaissance architecture, in which the circle's perfection connoted the divine.

Like sails on a three-master, the walls distinguish the church from the rectangular apartment blocks of the surrounding neighbourhood of Tor Tre Teste. But for all Meier's flamboyance, his works retain a purist's taste for white, and that sine qua non of classic modernism: the grid. "It's a scaling device," he says. "The grid in the concrete has to do with the way it's made, the whole idea of the pre-cast units coming together – it's not a monolithic surface, it's pieces in tension pulling together to make the shell."

The church's windows continue this pattern, but unlike the seductive white concrete, they have the ordinariness of corporate curtain walling. Meier prickles at the comparison: "It's as though you're setting up a false polemic that lack of ornament somehow isn't good or isn't appropriate for a church. It's a grid that's related to the grid of the shells – one thing dictates another."

However, he did consider stained glass. "I thought about it a lot but, you know, there's so much colour that it just doesn't need it."

E Compared with the darkness of most Roman church interiors, the Jubilee Church is luminous. Only one window, recessed above the altar, deviates from the rational clarity of the glazing and hints at religious mystery. But Meier is matter-of-fact about it: "It's a way of narrowing the light, I guess."

Designing for the Catholic Church meant Meier had to familiarise himself with its rituals and traditions but, in characteristically laid-back style, he gives no indication that this presented a challenge. "I had to learn things I didn't know, and occasionally if something wasn't quite right, I was informed."

His client seems to have been satisfied. "I presented the design to the Pope after I won the competition and he expressed enthusiasm for what he saw …
He didn't offer any criticism."

The Jubilee Church was the first of the 50 to be commissioned but the last to be completed. As construction work on the 2500 m2 building began in 1998, it must have proved more difficult than Meier had anticipated. "Have you ever spent time in Rome?" he asks. To this old hand – especially when in Rome – delays are par for the course. "When I started the Getty [the $1bn museum he designed in Los Angeles], they asked me if it would be finished in three years.

I said no, it would probably take 10 years. Well, it took 15. Sometimes it just takes longer than expected."

The cost of the project spiralled from $5m to $8m. Meier laughs off one report that it was nearer to $25m, saying: "Well, maybe it's worth that much now."

In the end, though, gratification came in the form of thousands of locals queueing up to get inside the church. At the inaugural mass, Meier was moved to see the building in action. "I thought it was amazing. I was thrilled to be there," he says. "It was the first time I had ever been to a mass. I shouldn't tell you that, but it's true."