The Pope is dead, the cardinals are locked in for a conclave, and the four favourites to succeed him have vanished. A revived secret society, the Illuminati, promises to kill one of them every hour, each at an "altar of science" for one of the four elements, Earth, Air, Fire and Water, along a hidden Path of Illumination marked out by Bernini. Somewhere in the Vatican, a stolen canister of antimatter is hidden. That's Dan Brown's novel Angels and Demons, from 2000, which Ron Howard filmed in 2009. Robert Langdon and the scientist Vittoria Vetra race across Rome to stop it. This walk follows their trail to all four altars, but in the order the streets allow: Earth, Fire, Water, then the Illuminati's lair, and Air with the finale at the end. Along the way, a second story runs underneath: who the real Bernini was, and why he could never have been one of the Illuminati. This is an unofficial walk, not made with or endorsed by Dan Brown, his publishers or the filmmakers. It's one of our self-guided walking tours, and a long one: about 6.2 kilometers from Piazza del Popolo to St Peter's Square.

Before you set off

This is a long walk. The walking alone takes about an hour and a half, around 88 minutes for the 6.2 kilometers, so with stops, allow at least two and a half hours. Start at Flaminio, on Metro Line A, right by Piazza del Popolo. You finish in St Peter's Square, and Ottaviano, also on Line A, is about a kilometer to the north. The route is mostly flat, with a gentle climb toward the Quirinal Hill and a descent after it. Expect cobbles and crowds, wear good shoes, and in summer carry water.

Four stops are working churches. Their opening hours vary, and every stop on this walk works from outside, so you lose nothing if a door is shut. If you do go in, be quiet and respect services. The Pantheon has ticketed entry. Check before you go.

Santa Maria del Popolo

You're in Piazza del Popolo. Find the church of Santa Maria del Popolo on the north side of the square. That position matters, because Dan Brown gets it wrong: the novel puts the church in the southeast corner.

This is EARTH, the first altar. In the novel, Langdon and Vittoria find the first missing cardinal inside, in the Chigi Chapel, the second chapel on the left. He is half buried, with earth in his mouth. Then Langdon spots a statue by Bernini, Habakkuk and the Angel, and the angel points the way on.

The chapel is real, and its story spans more than a century. Raphael designed it for the banker Agostino Chigi, starting in 1513, including the pyramid-shaped tombs. In the 1650s, Bernini completed it for a later member of the same family, Pope Alexander VII Chigi. Brown also buries Alexander VII in this chapel. He lies in St Peter's.

If the church is open, there's more inside: two paintings by Caravaggio, from around 1601, in the Cerasi Chapel.

You'll see none of this in the film. Rome's diocese said it would not let the crew film here or at the second church on our walk. A spokesman, Monsignor Marco Fibbi, said the film handled religious themes in a way at odds with common religious feeling. The interiors were rebuilt on sets.

Before we follow the angel, a word about the novel's history. Its tale of a church purge of scientists is fiction, and so is its Bernini of the Illuminati. We'll come back to that at the fifth stop.

Now walk southeast along Via del Babuino, the straight street from the corner of the square, all the way to Piazza di Spagna. About ten minutes.

Spanish Steps

You're at the foot of the Spanish Steps. In front of them sits a fountain shaped like a half-sunk boat: the Barcaccia.

No murder here. This is a link stop, to meet the real man the novel turns into a secret agent. The Barcaccia is by Pietro Bernini, working with his son, Gian Lorenzo. Gian Lorenzo is the Bernini of the novel. Look how low the fountain sits. It was set low to make use of the weak water pressure here. That's the real Bernini in miniature: a working sculptor, solving a practical problem.

Gian Lorenzo went on to fill Rome with fountains, churches and statues, many of them for popes. He died here in Rome, on the 28th of November 1680, aged 81. Keep that date in mind. It matters at the fifth stop.

In the novel, after Earth, the second cardinal dies at Air, in St Peter's Square. We're saving Air for the end of the walk, where it fits the streets and the story's finale. Next on our route is the Bernini fountain the novel uses as a signpost to Fire. From the Barcaccia, walk south along Via dei Due Macelli, then turn left up Via del Tritone, which climbs gently to Piazza Barberini. About eight minutes.

Triton Fountain

Triton Fountain in Piazza Barberini, Rome

You're in Piazza Barberini. In the middle stands Bernini's Triton Fountain. Triton, a sea god, blows a conch, on a shell held up by dolphins. Look closely and you'll find bees, the emblem of the Barberini family.

Bernini made it in 1642 and 1643 for Pope Urban VIII, a Barberini, and his great patron. This is the real relationship behind Bernini's career. He wasn't hiding messages from the Church. He was working for the papacy, openly, and the pope's family bees are right there on his fountain.

The novel sends Langdon to this square looking for the Fire church, Santa Maria della Vittoria, and places the church right here. It isn't here. It's a few hundred meters further on, on Via XX Settembre, and you're about to walk there.

Walk up Via Barberini, the wide street climbing northeast from the square, to where it meets Via XX Settembre. The church is a few steps further on, along Via XX Settembre. About seven minutes.