The cry of the crowd. The roar of a lion.  The clash of metal. Starting in 80 CE these sounds rang  through the stands of the Colosseum. On hundreds of days a year, over 50,000 residents of Rome and  visitors from across the Roman Empire would fill the stadiums’ four stories to  see gladiators duel, animals fight, and chariots race around the arena. And for the grand finale,  water poured into the arena basin, submerging the stage for the  greatest spectacle of all: staged naval battles. The Romans’ epic, mock maritime  encounters, called naumachiae, started during Julius Caesar’s reign  in the first century BC, over a hundred years before the  Colosseum was built. They were held alongside other  aquatic spectacles on natural and artificial bodies  of water around Rome up through Emperor Flavius Vespasian, who began building the Colosseum in  70 CE on the site of a former lake. The Colosseum was intended to be a symbol  of Rome’s power in the ancient world, and what better way to display that power than a body of water that could drain  and refill at the Emperor’s command? Vespasian’s son Flavius Titus fulfilled  his father’s dream in 80 CE when he used war spoils to  finish the Colosseum– or as it was known at the time,  the Flavian Amphitheater. The grand opening was celebrated with 100  days of pageantry and gladiatorial games, setting the precedent for programming  that included parades, musical performances, public executions,  and of course, gladiatorial combat. Unlike the games in smaller amphitheaters  funded by wealthy Romans, these lavish displays of Imperial power  were financed by the Emperor. Parades of exotic animals, theatrical  performances, and the awe-inspiring naumachiae  were all designed to bolster faith in the god-like Emperor, who would be declared a god  after his own death. It’s still a mystery how engineers flooded the arena to create this aquatic effect. Some historians believe a giant  aqueduct was diverted into the arena. Others think the system of chambers  and sluice gates used to drain the arena, were also used to fill it. These chambers could’ve been filled  with water prior to the event and then opened to submerge the stage under more than a million gallons of  water, to create a depth of five feet. But even with all that water, the Romans had to construct miniature  boats with special flat bottoms that wouldn’t scrape the Colosseum floor. These boats ranged from 7 to 15  meters long, and were built to look like vessels  from famous encounters. During a battle, dozens of these ships  would float around the arena, crewed by gladiators dressed as the  opposing sides of the recreated battle. These warriors would duel across ships; boarding them, fighting, drowning,  and incapacitating their foes until only one faction was left standing. Fortunately, not every watery display  told such a gruesome story. In some of these floodings, a submerged stage allowed chariot  drivers to glide across the water as though they were Triton, making waves  as he piloted his chariot on the sea. Animals walked on water, myths were  re-enacted by condemned prisoners, and at night, nude synchronized swimmers  would perform by torchlight. But the Colosseum’s aquatic  age didn’t last forever. The naval battles proved so popular they  were given their own nearby lake by Emperor Domitian in the early 90s CE. The larger lake proved even  better for naumachiae, and the Colosseum soon gained a series  of underground animal cages and trap doors that didn’t allow for  further flooding. But for a brief time, the Flavian Emperors controlled the  tides of war and water in a spectacular show of power.