The Colosseum or Coliseum, originally the Flavian Amphitheatre (Italian: Anfiteatro Flavio or Colosseo), is the most famous monument of Ancient Rome. It is an elliptical amphitheater in the center of the city of Rome, Italy, the largest ever built in the Roman Empire. Colosseum is one of the greatest works of Roman architecture and engineering.

Occupying the marshy site of a lake in the grounds of Nero’s palace, the Domus Aurea, just east of the Roman Forum, its construction started between 70 and 72 AD under the emperor Vespasian and was completed in 80 AD under Titus, with further modifications being made during Domitian's reign (81–96).

Deadly gladiatorial combats and wild animal fights were staged free of charge by the emperor and wealthy citizens for public viewing.

Vespasian was a professional soldier who became Roman emperor in AD 69, founding the Flavian dynasty.The name "Amphitheatrum Flavium" derives from this family name ("Flavius, from the gens Flavia), but it was called the Colosseum after a truly colossal, 100 feet high, gilded bronze statue of Nero as the God of the Sun that stood in the vicinity until the end of the 6th century.

Colosseum is one of several similar amphitheaters built in the Roman Empire, and some survive at El Djem in North Africa, Nimes and Arles in France and Verona in northern Italy.

The building's core is constructed of brick and a relatively soft, porous tufa. The Colosseum was faced with travertine marble, later favored also by Michelangelo for his sculptures, accented with hundreds of statues and had a velarium – an ingenious system of sail-like awnings rigged on ropes manned by imperial sailors – to protect the audience from the sun and rain. Originally the Colosseum had three stories, but a fourth was added by Alexander Severus when he refurbished the building around 230 AD.

The bottom three stories have 80 arches each; the stories are separated by a thin architrave (a horizontal band running around the entire Colosseum).

The columns in one story line up exactly with those in the story above it.

The bottom story has 80 entrance arches, each of which is separated by a Doric column (the columns are engaged, which means the column shafts are actually part of the wall making it impossible to walk behind the columns).

The second story has engaged Ionic columns, and the third has Corinthian.

The fourth story is a solid wall with thin Corinthian pilasters (rectangular columns that are also engaged). The space between the pilasters is filled alternately with 40 small, rectangular windows and 40 bucklers (now lost).

Holding up to 73.000 spectators, entrance to the Colosseum was regulated through a ticket system, with each ticket indicating where the holder should go through the internal passages and corridors to find his or her seat.

The stadium was built in the form of an ellipse , with tiers od seats for different social classes around a vast central arena.

After the splendor of imperial times, the Colosseum was abandoned, and in turn it became a fortress for the medieval clans of the city, a source of building materials, a picturesque scenery for painters, a place of Christian worship.

Today it is a challenge for the archaeologists and a scenario for events and shows.