Rams

Many of the metal ends (rostrums) on the end of Roman and Carthaginian rams survived, and a previously unlocated naval battle is now known. One end of the rostrum was a hollow socket to fit on the end of the wooden prow. The front of it was split into several shovel-like spikes for poking holes into other ships, with gaps between to help snag the enemy's oars if you wound up skimming alongside instead of hitting squarely.

Strangely, the divers have found that the hollowed-out insides are often filled with small objects such as coins. This, he says, is the work of octopuses, who have turned the rostrums into temporary dens. They have a magpie-like tendency to pick up treasure – and fill their homes with trinkets. "They are inveterate collectors," he says. "They'll take anything they can get their hands – or tentacles – on."