Up on the breezy Aventine hill, we joined the queue in the Piazza of the Knights of Malta and peeped through the famous Aventine keyhole to see the dome of St Peter’s across the Tiber. Nobody seemed to look hard at the portal structure or the piazza walls. So they missed seeing some of the only architecture of the legendary engraver, architect and archaeologist Giovanni Battista Piranesi. Granted, much of it was shrouded in scaffolding, but the twining designs and amazingly sharply defined plasterwork friezes on the gatehouse, and several funerary-style obelisks should interest any Piranesi fan. They cleverly incorporate symbols of the Knights of Malta, allude to the Aventine’s supposed likeness to a ship, and bring some of Piranesi’s research on ancient roman funerial monuments into 18th century reality.