One may be aware that the Colosseum used to have a retractable floor - impressive engineering for such a building 2,000 years old! The Romans were certainly renowned for their superb engineering. But that's not all, before they built the retractable floor, they built the Colosseum in such a way that they could flood the floor for mock naval battle reenactments.
The word for these staged naval combats was "naumachia". In Ancient Rome, the word referred to both the staged naval battles and the basin or arena where they were held. They were very large and deadly affairs.
History of The Bloody Roman Naumachiae
The first known naumachia was held by Julius Caesar in 46 BC in Rome and was held to celebrate his quadruple triumph (Caesar had the habit of winning his battles). To stage these naval engagements, he dug a basin near the River Tiber.
First Naumachia: By Julius Caesar In 46 BC
The basin was able to hold actual Roman biremes, triremes, and quinqueremes. The massive event involved 2,000 combatants and 4,000 rowers (all of these were prisoners of war) and they were forced to fight (the bad old days before the Geneva Convention).
Numbers: 2,000 Combatants and 4,000 Rowers
44 years later Augustus gave another even larger and grander spectacle for the inauguration of the Temple of Mars Ultor. Mars was the god of war and the most prominent god of the Roman military - so his celebration was always going to be bloody.
The staged battle enacted a battle between the Greeks and Persians. The basin was 400 by 600 yards and staddled the Tiber. It was claimed that this festival included 3,000 men fought - plus the thousands of rowers with 30 vessels with rams and some smaller boats.
Numbers: 3,000 Combatants Plus Rowers
The most epic of these battles was likely given by Emperor Claudius in 52 AD - this time in the Lake Fucine (and it was to celebrate the completion of the Roman tunneling and draining of the lake - it was the longest tunnel for thousands of years).
It is said that this battle included 100 ships and some 19,000 combatants (all prisoners condemned to death).
Numbers: 19,000 Combatants
Naumachiae Were Much Bloodier and More Expensive Than Gladiatorial Combats
These naumachia or naval re-enactments were much bloodier than gladiatorial combats. In gladiatorial combats, it was not a given the losing gladiators would die. Whereas gladiatorial combats were teams, bands, or individuals pitted against each other. Naumachiae were more akin to full-on armies fighting to the death, those in these battles typically lacked the specialized training of the gladiators.
Training: Combatants In Naval Battles Were Not Given The Same Training
They were very expensive and only reserved for special occasions tied to the emperor (like victories or particularly important feats of engineering).
The battle with the chariots in the Colosseum involving 50 or so combatants in the 2000 movie Gladiator is just small fry. Watching that scene looks bloody, but it was nothing on the scale of what the Romans could do.
The Naumachiae In The Colossuem
So when the Colosseum (itself built with the plunder of AD 70 sacking of Jerusalem) was inaugurated, Emperor Titus gave two naumachiae. These employed several thousand men, one of the events was held in the Augustinian basin and the other in the new Colosseum.
Colosseum Size: Measuring only 79.35 x 47.20 meters It Was A Bit Small For Such Large Spectacles
Reduced: The Limited Size Meant That The Colosseum Could Not Hold Large Engagements With Warships
Mystery: It is Still a Mystery How The Colosseum was Waterproofed
In 80 AD, the Colosseum hosted mighty naval battles that drew in spectators of Rome and visitors from across the Roman Empire. They would come to see gladiators duel, animals fight, and chariots race around the arena. At the end of this Roman entertainment bathed in blood, water would pour into the area's basin. The stage would submerge under around 5 feet of water.
The stage would then be set for the greatest spectacle - staged naval battles! Ted-Ed by Janelle Peters made an excellent short video on how this happened and what is known about it.
There were likely more held by Emperor Domitian. One was held around 85 AD was held in the Colosseum and another in 89 AD was held in a basin outside of the Colosseum.
But soon after the naumachiae were held in the Colosseum the area's floor was reworked and a network of rooms was completed underneath the Colosseum (still visible today). After that, no more naumachiae were possible in the Colosseum.
It is debated if the ships in the Colosseum even floated - Ted-Ed asserts that special ships with flat bottoms were built for it so that they could.
Despite the floor of the Colosseum having been completely reworked since then, the tail-tale signs of the engineering taken to flood the Colosseum are still visible today.