The Colosseum, Rome, Italy

This is the largest amphitheater ever built in the Roman Empire and definitely one of the greatest achievements of Roman engineering. It only took eight years to finish this amazing structure that continues to stand as Rome’s most prestigious symbol for almost 2,000 years now. With a capacity of 50,000, the Colosseum was used for gladiator contests, animal hunts, re-enactments of famous battles and dramas. During the Middle Ages, it was used as a workshop, a fortress, a quarry and even a Christian shrine. Although it was affected by fires, earthquakes and many more forms of natural degradation, the Colosseum is still standing.

Being 615 feet (189 meters) long and 510 feet (156 meters) wide, the outer wall of the Colosseum is estimated to have required at least 100,000 cubic meters of travertine stone. For such a colossal structure, the architects of the Colosseo used access methods similar to those used by the modern stadiums nowadays: more than 80 entrances at ground level were designed and each one was numbered, as was each staircase.