When I was in Rome and visited the Colosseum, I did learn a few things:
1. If you take a picture of a Roman soldier, they expect you to give them some money.
2. If you see a set of toys horses randomly set up on the grounds, don’t get too close (even if you just want to take a picture) because you will be bombarded by the entrepreneur who is selling these fine horse replicas.
3. Gelato is delicious.
But I didn’t know the following:
During the early days of the Colosseum, ancient writers recorded that the building was used for naumachiae (more properly known as navalia proelia) or simulated sea battles. Accounts of the inaugural games held by Titus in AD 80 describe it being filled with water for a display of specially trained swimming horses and bulls. There is also an account of a re-enactment of a famous sea battle between the Corcyrean (Corfiot) Greeks and the Corinthians. This has been the subject of some debate among historians; although providing the water would not have been a problem, it is unclear how the arena could have been waterproofed, nor would there have been enough space in the arena for the warships to move around. It has been suggested that the reports either have the location wrong, or that the Colosseum originally featured a wide floodable channel down its central axis (which would later have been replaced by the hypogeum)
Claridge, Amanda (1998). Rome: An Oxford Archaeological Guide (First ed.). Oxford, UK: Oxford University Press, 1998. pp. 276–282
The Colosseum actually had awnings.
Under the summer sun, the windless interior of the Colosseum could reach appalling temperatures. Awnings overhead were essential to provide shade, and here as elsewhere the notice ‘vela erunt’ (‘there will be awnings’) would encourage spectators.
To provide shade over such a vast area was, however, a major challenge. All we can see now are the projecting stone brackets for awnings in the top story, three in each of the eighty bays. These supported 240 wooden masts, from which were suspended the system of ropes and stays from which the canvas awnings were hung. A company of sailors executed this complex operation.
(quoted from BBC’s website)