Fans of debate might recognize the -machia/-machy half of the word from logomachy, another name for a war of words. That -machia/-machy comes from the Greek machē, a war or battle.
The first syllable of naumachia comes from a root that lent itself to a number of words more common than logomachy, though it might seem a bit disguised here. Nau- stems from the Greek naus, ship. It's the same etymological root that gives us nautical, astronaut, and nautilus.
Naumachia/naumachy, then, is a ship battle — specifically a mock naval battle put on for entertainment. It's also the name of the watery arena where such a spectacle takes place.
 |
| Photo by Jon Olav Eikenes. |
The Colosseum, of course, was a gladiatorial arena, and these naumachies fit right in. According to the ancient poets and historians, they involved a number of boats manned by thousands of prisoners of war and those condemned to death. The men were set into two teams and pitted against one another on the water. So, although they were called "mock" naval battles, they were life-or-death ordeals for those forced to participate.
Now, I put on a pretty impressive reenactment of the Battle of Quiberon Bay in my bathtub, but I try to avoid spilling bathwater, much less blood, on the tile floor. So calling my bath-time battles naumachia is probably an exaggeration. The naumachies of ancient Rome were huge spectacles, with much better seating than you'll find around my tub.