Learn how the Romans might have developed a plumbing system to pump enough water into and out of the Colosseum to stage mock naval battles, in this video from NOVA: Building Wonders: Colosseum. Romans relied on aqueducts to supply their city with water. According to an early Roman author, they may have also used the aqueducts to fill the Colosseum with enough water to float flat-bottomed boats. While 40 input channels could have sufficiently flooded the arena’s floor, the recent discovery of an ancient drain may have revealed how the emperor’s engineers could have emptied the water to hold gladiator fights the same day.