Discover Sant'Ignazio di Loyola

Sant'Ignazio di Loyola has the most famous ceiling in Rome that is not in the Vatican, and the most famous part of it is a copy.

The church was built to a Jesuit's design. It was erected to the design of the Jesuit mathematician Orazio Grassi, on projects by Carlo Maderno and others, at the expense of Cardinal Ludovico Ludovisi, nephew of Gregory XV — as the inscription on the façade records.

The front is a deliberate quotation. The façade is inspired by that of the nearby church of the Gesù, with two orders of pilasters and Corinthian columns, a large window, pedimented niches and cartouches.

Inside, the plan is simple and the surfaces are not. The interior is a Latin cross with three intercommunicating chapels on each side, and the polychromy of the marbles, the stuccoes, the pictorial decoration and the richness of the altars give the whole a sumptuous magnificence.

The nave vault is the work of a Jesuit brother. Andrea Pozzo, of the Jesuit Order, painted The Ascent of St Ignatius into Paradise across it.

And the dome is not a dome. At the crossing Pozzo painted a false dome — a canvas 13 metres in diameter carrying the perspective effect of an architecture that is not there. The original, completed in 1685, was destroyed by a fire. What you look at now was faithfully reproduced in 1823 by Francesco Manno, working from the drawings and studies Pozzo left.

It is free, and it stays open late. Turismo Roma publishes the opening as Monday to Sunday, 9.00 to 23.30.

The architecture here is partly real and partly painted, and the painted part is the famous half.

The façade is a copy with a purpose. It is inspired by that of the nearby Gesù — two orders of pilasters and Corinthian columns, enriched by a large window, niches with pediments and cartouches. The Jesuit plan had become a recognisable type, and this front declares membership of it.

The plan is a Latin cross with linked side chapels. There are three chapels on each side, intercommunicating, so the flanks of the nave read as a chain of small spaces.

The decorative system is marble, stucco and paint working as one. The polychromy of the marbles, the stuccoes, the pictorial decoration and the richness of the altars are what the city singles out, and together they produce a surface with no neutral ground anywhere.

The crossing is the architectural event, and it is a canvas. Pozzo's false dome is 13 metres in diameter, flat, and carries a painted architecture calculated to read as a cupola from a single viewing point on the nave floor.

The nave vault does the same trick at length. The Ascent of St Ignatius into Paradise carries the built architecture upward into fictive architecture and then into open sky, so the join between stone and paint is deliberately hard to find.

And the thing to remember is the date of the surface. The dome canvas is Manno's reproduction of 1823, not Pozzo's 1685 original.

It was designed by a mathematician, and the ceiling is where that shows. The church was erected to the design of the Jesuit mathematician Orazio Grassi, working on projects by Carlo Maderno and others.

It was paid for by one cardinal. The expense was borne by Cardinal Ludovico Ludovisi, nephew of Gregory XV, as the inscription on the façade records — the funding is written on the building.

The dome was solved by painting rather than building. Rather than raise a cupola over the crossing, Pozzo supplied one as a canvas 13 metres in diameter, on which he produced the perspective effect of a fictive architecture.

That solution is also what made it replaceable. A painted dome on canvas can burn, and this one did — but it could then be reproduced in 1823 by Francesco Manno from the drawings and studies Pozzo had left. A built dome could not have been restored from drawings in the same way.

The decoration was executed by a member of the order. Andrea Pozzo was a brother of the Jesuit Order, so the painter of the vault was inside the institution that commissioned it.

Is there a charge? No. It is an active Jesuit church, free, with nothing to book.

What are the opening hours? Turismo Roma publishes Monday to Sunday, 9.00 to 23.30 — far later than almost any other church in Rome.

Is the dome real? No. It is a flat canvas 13 metres in diameter, painted by Andrea Pozzo with the perspective effect of an architecture that does not exist.

Is it Pozzo's original? No. His canvas, completed in 1685, was destroyed by a fire. The present one was faithfully reproduced in 1823 by Francesco Manno, from the drawings and studies Pozzo left.

Where do I stand to see it? On the marker set into the nave floor beneath the crossing. From anywhere else the painted architecture visibly skews.

What is on the nave ceiling? The Ascent of St Ignatius into Paradise, by Andrea Pozzo, a brother of the Jesuit Order.

Who designed the church? The Jesuit mathematician Orazio Grassi, on projects by Carlo Maderno and others, at the expense of Cardinal Ludovico Ludovisi, nephew of Gregory XV.

Why does the front look like the Gesù? Because it is inspired by it — two orders of pilasters and Corinthian columns, a large window, pedimented niches and cartouches.

When is mass? 18.30 Monday to Saturday; 11.30 and 18.30 on Sundays and feast days.

How long does it take? About thirty minutes.