The only work Michelangelo ever signed

Michelangelo made the Sistine Chapel ceiling, the David and the dome of St Peter's, and he signed none of them. He signed one work in his whole life, and it's just inside the door of St Peter's Basilica, behind a sheet of bulletproof glass.

It's the Pietà: Mary holding her dead son across her lap, carved from a single block of marble. Michelangelo was in his early twenties when he made it. A French cardinal living in Rome ordered it for his own tomb, and the contract promised "the most beautiful work in marble that exists in Rome today". He finished it around 1499.

A name in the night

Look at the band of cloth running diagonally across Mary's chest. His name is carved along it, in Latin.

The art historian Giorgio Vasari, who knew Michelangelo, says why. Soon after the statue went on show, Michelangelo overheard visitors saying it was the work of another sculptor, from Milan. That night he came back with a lamp and his chisels and cut his name across her sash.

He never signed anything again. Vasari may have polished the story, but the signature is real, and you can read it from where you stand.

One more thing people notice: Mary looks younger than her son. When people asked about it, Michelangelo is said to have answered that purity keeps a woman young.

Why it's behind glass

For nearly five hundred years, the Pietà stood in the open, close enough to touch. Then, on 21 May 1972, a man named László Tóth climbed over the railing with a hammer, shouting that he was Christ. He struck the statue about fifteen times before people pulled him away.

Mary's left arm was broken off at the elbow, and her nose and one eyelid were smashed. Restorers gathered the fragments and spent months putting her back together. Some pieces had been pocketed by onlookers, and a few never came back.

The Pietà returned in 1973, behind the glass you see today, and it has been seen from that distance ever since.

Where to stand

Go in through the main doors of St Peter's and turn right. The Pietà is in the first chapel on the right. Stand a little to one side of the centre and look along the sash across Mary's chest: the letters run with the fold of the cloth.

Then walk about 100 metres up the nave to Bernini's huge bronze canopy over the main altar, and look for the bees climbing its columns. They're the badge of the pope who paid for it, and there's a joke about him that Romans still repeat.

Hear it where it happened

The Trevlo tour of St Peter's starts in the square, at the obelisk, and takes you to the Pietà, the canopy and up into the dome. Six stops, about twelve minutes of listening, at your own pace.

The first stop is free to play on this page, and your first tour in the app is free.