From above, Piazza San Pietro looks like a giant keyhole. The square's creator, Bernini, described the double colonnade as 'the motherly arms of the church'. He'd planned for the square to gob-smack pilgrims as they emerged from the tangle of medieval streets, an effect spoilt when Mussolini bulldozed Via della Conciliazione through the area. Caligula shipped in the central obelisk from Heliopolis, and it was later used by Christian-culling Nero as a turning post at his chariot-racing circus.