[Ruy Dias de Bivar]

I have read that they had a way to flood the arena and stage small naval battles. Wonder how they kept the water out of the underground tunnels.

[hinckley buzzard]

That was Nero’s huge artificial lake built as part of his palace complex. After his death, Vespasian had it filled in and the Coliseum built on top of where it had been.

[Pilsner]

I have read that they had a way to flood the arena and stage small naval battles. Wonder how they kept the water out of the underground tunnels.

The underground complex, or at least the part beneath the playing, err, slaying area, or arena, was installed as part of an upgrade ordered by Domitian. After that, it was no longer possible to flood the arena for naval battles.