It was built in 1480, but Pietro da Cortona gave it its present, Baroque appearance. He built a new facade, in front of which stands a semicircular porch, adorned with columns, topped by two tympanums, one triangular-shaped and the other round. These are enclosed by concave wings and the whole structure is a combination of harmonious movement, overlooking a handsome square with coloured facades. The very simple cloister is by Bramante. Inside, the four Sybils are by Raphael.