Mock naval battles in the Colosseum? | AskHistorians Archive Observer

Oh this is a cool question on Roman engineering! I'm just sorry that I didn't get to it earlier. Let's see what we can do, eh?

So first off, we want to start with a quick discussions of these naval battles, otherwise known as naumachiae. The Romans were quite fond of naumachiae - after all, they were a people who loved spectacle, and bringing a sea battle to land was one heck of an achievement in that regard. The apparent first of these games in Rome was held by Julius Caesar, during his set of triumphs, when he dug a massive hole next to the Tiber, filled it with water, and staged a massive mock battle, which Suetonius describes thusly:

For the naval battle a pool was dug in the lesser Codeta and there was a contest of ships of two, three, and four banks of oars, belonging to the Tyrian and Egyptian fleets, manned by a large force of fighting men. Such a throng flocked to all these shows from every quarter, that many strangers had to lodge in tents pitched in streets or along the roads, and the press was often such that many were crushed to death, including two senators.

Appian supports this, claiming that 2,000 combatants and 4,000 oarsmen were involved. Needless to say, it was popular! So popular, in fact, that his adopted son, later known as Augustus, decided to host one of his own, ostensibly to celebrate the completion of the temple of Mars the Avenger. He helpfully brags about the achievement in his autobiography:

I gave the people a spectacle of a naval battle, in the place across the Tiber where the grove of the Caesars is now, with the ground excavated in length 1,800 feet, in width 1,200, in which thirty beaked ships, biremes or triremes, but many smaller, fought among themselves; in these ships about 3,000 men fought in addition to the rowers.

Coincidentally, it was also held at the same time as the completion of the aqueduct to the Alsietina, which was to later provide irrigation. That aqueduct is also described in texts (whee, quote dropping!) by Frontinus, whose writing is excellent for understanding the efforts of Roman engineers:

What reason moved Augustus, the most farsighted of emperors, to introduce the Aqua Alsietina, which is called the Augusta - water without favor, indeed hardly beneficial, and so never channeled for public use - I do not entirely understand; unless perhaps when he undertook to build the Naumachia, so that he should not draw upon more salutary waters at all, he introduced it in an isolated system and then, because it proved to be excessive for the Naumachia, he granted concessions to adjacent gardens and to private citizens for irrigation. By necessity, however, whenever the bridges are being repaired and the waters from the near bank are cut off, it is customary in the Transtiberine region for waters from it to serve as a supplement to the public fountains.

The pond of Augustus (if we want to call it a pond, it's basically a lake), quickly developed into what was alternatively called the "Naumachia" and the "Grove of the Caesars." It was a popular destination, filled with gardens and a particularly enormous number of brothels. Tiberius was known to have used the area as a nice, secluded spot for temporary relaxation, and further naumachiae were held there, on account of the convenience of the location. There's also a good amount of interesting data for exactly how long it would take to fill or drain the lake, how much the aqueduct itself carried, and so on. But that's not what we're here to talk about. We're here to talk about the Flavian Amphitheater - today simply known as "The Colosseum."

The first "purpose-built" amphitheatre in Rome that supposedly held naval battles (we're not sure about the logistics of this, but primary sources do agree) was built by Nero, when he built a wooden structure on the Campus Martius that was apparently used for such a purpose. It wasn't particularly permanent: wooden structures seldom are, compared to monumental stone architecture. The Colosseum itself was built years later, and the Julio-Claudians generally stuck to lakes (Claudius didn't hold his naval battles in the Grove, but that's partly because he was showing off his own engineering marvel: the draining of the Fucine Lake. Which is another tangent, but his battle apparently involved 19,000 combatants. The accuracy of these numbers may not be perfect, though).