The arena in Pula, Croatia is not a copy of the Colosseum in Rome. It's an original structure. In fact, the masonry work in some area even started before the Colosseum.
The Pula Arena is one of the best-preserved Roman amphitheaters, notable for having all four side towers fully preserved, unlike the Colosseum.
It was designed to accommodate roughly 20,000 spectators, making it smaller than the Roman Colosseum.