The most famous and important monument, the starting and ending point of every sightseeing tour is the Amphitheater, popularly called the Arena of Pula, which was once the site of gladiator fights. It was built in the 1st century AD during the reign of Emperor Vespasian, at the same time as the magnificent Colosseum in Rome.
The ground plan is elliptical, the longer axis measuring about 130 m and the shorter one about 100 m. Gladiator fights took place in the central flat area called the arena, while the spectators could sit on the stone tiers or stand in the gallery. It is believed that the Amphitheater could seat about 20,000 spectators. Local limestone was used for its construction. In the Middle Ages, it was the site of knights tournaments and fairs.
Today, it is the venue for many different events – Pula Film Festival, various concerts, opera, ballet, sports competitions… since its capacity is about 5000 spectators. http://www.pulainfo.hr/where/arena-amphitheater-2