Today the arena floor no longer exists, though the hypogeum walls and corridors are clearly visible in the ruins of the structure. The entire base of the Colosseum covers an area equivalent to 6 acres (160,000 m²). There are also tunnels, still in existence, configured to flood and evacuate water from the Colosseum floor, so that naval battles could be staged prior to the hypogeum's construction. Recent archaeological research has shown evidence of drain pipes connected to the City's sewer system and a large underground holding tank connected to a nearby aqueduct.