The Colosseum in Rome was remarkable for a few reasons upon its construction in the first century C.E. The most obvious was its size. At four stories high and with 80 arched entrances, the amphitheater could seat 50,000 or more people, then and now a striking achievement.Second was its design. Amphitheaters of the period were usually built into slopes for support. In contrast, the Colosseum is completely freestanding, supported by several layers of varied building materials and a complex vault system. Archaeologists believe the Colosseum was outfitted with amenities like water fountains and latrines. There was even a retractable awning system that required hundreds of hands to operate.The Colosseum is still a dominant fixture in the Roman cityscape. It was named one of the New Wonders of the World in 2007.Who built the Colosseum?The arena was built between 70 and 80 C.E. on the orders of Emperor Vespasian. His Flavian dynasty ruled from 69 to 96 C.E., succeeding the despotic Nero after a tussle with other throne hopefuls. Vespasian ordered the Colosseum to be built on the site of Nero’s private estate, which he’d constructed after the infamous fire of 64 C.E. Vespasian’s decree returned to the Roman public what had been a symbol of imperial wealth.Vespasian died in 79 C.E., before the Colosseum was completed. His son Titus dedicated the building in 80 C.E., inaugurating it with 100 straight days of gladiator games. An upper level was added several years later by Vespasian’s second son, Domitian.The Colosseum, RomeEmanuele Cremaschi/Getty Images.Why is it called the Colosseum?Actually, it’s not because of its colossal size. A colossus, or giant statue, once stood on the site. Initially built as a likeness of Nero, it was adapted by his successors to instead depict the Roman sun god Sol. The statue’s fate is unclear.What was it used for?The Colosseum’s most famous use was for gladiator games. The fighters were usually slaves or prisoners of war, and the games a form of public degradation. Besides gladiator battles, the arena was used for mock naval battles (for which the amphitheater was reportedly filled with water), theater, and public executions. However, no historical record exists to back up the long-standing claim that Christians specifically were martyred there.Why did the Colosseum fall out of use?Gladiator games fell out of vogue in the Western Roman Empire even before the empire collapsed in 480 C.E; the last recorded depictions of gladiator games at the Colosseum date to the fifth century. By the late sixth century the Colosseum was no longer in use as an amphitheater at all. The empire’s fall accelerated the site’s decline.What happened to the Colosseum between the Roman period and the present?After its discontinuation as a public venue, the amphitheater was used for Christian worship. A chapel was added, the main floor became a cemetery, and other spaces were repurposed as residences and businesses. Eventually aristocratic families seized the building and used it as a fortress.The building was all but abandoned after suffering a partial collapse during an earthquake in 1349. For the next four centuries, it became a quarry for construction projects around Rome. Materials from its facade were used to build St. Peter’s Basilica, the Palazzo Venezia, and other landmarks.In 1749 Pope Benedict XIV, believing Christians had been martyred there, declared the Colosseum a holy site. This put the brakes on widespread looting and human-inflicted erosion of the site. The following century, Pope Pius VIII led efforts to formally preserve the Colosseum. By then, nearly two-thirds of the original building had been destroyed; what visitors see today is a restoration, attracting some seven million tourists per year.