The Colosseum didn’t exist in Nero’s day when there really was persecution and prosecution and execution of Christians in Rome (and later during Domitian’s paranoid reign as well). The Colosseum was built by the Flavians, in particular Titus. Here is the Wiki summary… which is correct.
“Construction began under the emperor Vespasian in 70 AD, and was completed in 80 AD under his successor and heir Titus. Further modifications were made during the reign of Domitian (81–96). These three emperors are known as the Flavian dynasty, and the amphitheatre was named in Latin for its association with their family name (Flavius) i.e. the Flavian amphi-theatre is what it was called.
The Colosseum could hold, it is estimated, between 50,000 and 80,000 spectators, and was used for gladiatorial contests and public spectacles such as mock sea battles, animal hunts, executions, re-enactments of famous battles, and dramas based on Classical mythology. The building ceased to be used for entertainment in the early medieval era. It was later reused for such purposes as housing, workshops, quarters for a religious order, a fortress, a quarry, and a Christian shrine.”
Today, of course it is a mere shell of its former glory, but still it is enormous and a major tourist attraction.
Notice all the holes in the walls— from where the large bits of marble facade were hung.
And here is what the interior looks like today. What you are actually seeing is the sub-surface corridors in which animals etc. were kept, and by means of some of which water was used to flood the colosseum for mock sea battles (think tractor pull in Rupp arena, with tons of sand brought in :).
No that man is not a promoter of gladiatorial contests looking for a last minute replacement. Gladiatorial contests were something specifically Roman. The Greek found it barbaric.