The amphitheatre on a lake

There was a lake here once. After the great fire of 64, the emperor Nero had an enormous palace complex built for himself, the Domus Aurea, with an artificial lake in the valley to look out over. When he fell from power, his successors drained that lake and raised the largest public building in the empire on the very spot where the emperor had kept his private garden. Everyone could read that message.

It was paid for with the spoils of Jerusalem, where the Roman legions had plundered the temple in the year 70. It opened in the year 80, with a hundred days of games.

Around fifty thousand people fit inside, let in through eighty entrances numbered to match the number on their ticket, so that a packed arena could empty out in minutes.

The difference between the two sides is worth a look. The north side still stands four storeys high, while the south side is a broken-off edge. An earthquake in 1349 brought that half down, after which Roman families spent centuries quarrying the rubble for their palaces and churches.

The thousands of holes in the walls come from something else. Metal clamps held the blocks of travertine together, and in the Middle Ages that iron was chiselled out one piece at a time to be melted down.

We walk around the arena heading south, towards the tall arch between the Colosseum and the Palatine.