The Great Bath is a massive pool, lined with 45 sheets of lead, and filled with hot spa water. It once stood in an enormous barrel-vaulted hall that rose to a height of 40 metres. For many Roman visitors this may have been the largest building they had ever entered in their life. The bath is 1.6 metres deep, which was ideal for bathing, and it has steps leading down on all sides. Niches around the baths would have held benches for bathers and possibly small tables for drinks or snacks. A large flat slab of stone is set across the point where hot water flows into the bath. It is known today as the diving stone.