The Coliseum (also spelled Colosseum), otherwise known as the Flavian Amphitheater (Colosseo and Anfiteatro Flavio in Italian), is the closest thing to the idea of symbol of Rome, or, in all cases, of Imperial Rome. Despite the fact nowadays it is more of a shell of the old monumental structure, it remains one of the greatest architectural and engineering achievements of ancient Rome (in fact, the largest amphitheater ever erected by the Romans).
The Coliseum was built in only 8 years, between 72 AD and 80 AD. The construction works were commissioned by Emperor Vespasian, just to be completed under Emperor Titus. Its ancient name (Amphitheatrum Flavium) hints on the fact the patrons of the structure were all members of the Flavian dynasty (including Domitian, who followed Titus to the reign of Rome, under whom sundry modifications were made).
The prestige of this landmark of Rome is based not only on its architectural merits, but also on the fact from its construction until the Middle Ages, it was used as a public entertainment venue: the Romans would come to the amphitheater and enjoy the bloody battles between gladiators, between gladiators and beasts, theater representations focusing on the Greek and Roman mythology and on the historical deeds of their predecessors. The Coliseum is also the place where, as it was occasionally maintained, the early Christians were fed to the lions, though the claim was proven to be unfounded. The popularity of the venue with the large Roman public is proven by the fact that in its heydays, under Domitian, the theater came to be able to accommodate about 50,000 spectators.
The elliptical structure slowly decayed as from the Middle Ages, generous amounts of travertine ripped off the Coliseum being turned into construction material for other edifices in Rome. After centuries of neglect, when it was more of a chaotic quarry, the Coliseum assumed a new role in the life of the Romans: since the mid 18th century (under Pope Benedict XIV), it was declared a sacred site due to the alleged martyrdom of the early Christians, such that its improper exploitations ceased. At present, this wide ancient edifice is opened to visits being, in fact, one of the most iconic landmarks of Rome. It is occasionally home to sundry music and entertainment happenings, though it is not considered safe for such events (in all cases, for larger events where the public attending is expected to be numerous).
The Coliseum, together with the Roman Forum and the Arch of Constantine, form a quite compact tourist area of Rome, impossible to miss out by visitors who want to spend a complete Roman vacation in the capital of Italy. The sight can be visited all the year round, but there are significant seasonal schedule variations to be taken into account. The admission amounts to a little over 15 euros (full ticket).