Michelangelo was only 24 years old when he finished the Pietà - still very young for such a huge and difficult project. He chose a type of marble from a quarry in Carrara, Italy, famous for being extra white and smooth. The block weighed several tonnes when it arrived, and Michelangelo turned it into something that seems almost weightless.
Every fold of cloth, every strand of hair, and every finger on both figures was carved with small chisels and special abrasive stones to create an incredibly smooth surface. Michelangelo spent years polishing the marble until it shone. Art experts who have studied it say the folds in the fabric are so realistic that people have tried to touch them to check they are really stone.
The Pietà is the only work that Michelangelo ever signed. After it was finished and put on display, some visitors thought it had been carved by a different, older sculptor. According to the story, Michelangelo returned at night and carved his name along the strap across one of the figures - the only time he signed any of his sculptures.