"The sixth-largest Roman amphitheater still standing today, the Pula Arena is Croatia’s most magnificent classical monument—and reason enough to check out Pula, Istria’s main city. Built in the 1st century C.E. during the rule of Emperor Vespasian, this oval-shaped stunner once hosted gladiator fights and could hold up to 23,000 spectators. Today, visitors can roam freely through the small underground chambers and enjoy the sweeping ocean views. During the summer months, the arena doubles as the most imposing stage in all of Croatia , hosting several concerts and film festivals."