In the Epoch Times we read a touristy piece on Turkey, inter alia:

From reading the well-researched gallery cards, the relationship between gladiator and spectator becomes apparent. The highly evolved Roman culture had also developed a vicious thirst for life, victory and death. Gladiator games had become so popular throughout the Empire in cities such as Ephesus that some noblemen were known to sell themselves into slavery for a fight in the arena. At least seven emperors, including Nero and Caligula, are known to have entered the arena as gladiators. When Trajan became Emperor, he organized 10,000 gladiators to fight within one week.

I'm going to have to dig out some books on this one, but for the life of me I can't think of seven emperors who entered the arena ...