Originally the Roman Colosseum had a wooden floor that covered an elaborate 2-level subterranean network of tunnels and cages where gladiators and animals were housed before the contests began. The vertical shafts, seen in the center of the photo, provided instant access to the arena from the underground. I was amazed to see the re-constructed mechanical elevators with pulleys that were used to raise and lower men and beasts in and out. It was also possible to flood the interior for mock sea battles.
Not much has changed in the last 2,000 years. I had a tour of the new Sofi Stadium in Los Angeles last year before it opened. It's really just a modern technological version of the original. It seats 100,000, complete with various levels of status seating and a maze of underground tunnels. We still have our "gladiators" on the field but at least there are no wild animals... as far as I know. Best viewed on black.
