The Colosseum

The Colosseum or Flavian Amphitheater was begun by Vespasian, inaugurated by Titus in 80 A.D. and completed by Domitian. Located on marshy land between the Esquiline and Caelian Hills, it was the first permanent amphitheater to be built in Rome. Its monumental size and grandeur as well as its practical and efficient organization for producing spectacles and controlling the large crowds make it one of the great architectural monuments achieved by the ancient Romans.
All the Romans liked to go to the theater to watch concert and plays. They also liked to go to the stadium to watch chariot races and to the amphitheater to watch sports. Among all these, perhaps going to the amphitheater i.e. Coliseum was the most popularly accepted by the Romans. Gladiatorial combats, fights with beasts and other fights were held in the Coliseum.
The amphitheater is a vast ellipse with tiers of seating for 50,000 spectators around a central elliptical arena. Below the wooden arena floor, there was a complex set of rooms and passageways for wild beasts and other provisions for staging the spectacles. Eighty walls radiate from the arena and support vaults for passageways, stairways and the tiers of seats. At the outer edge circumferential arcades link each level and the stairways between levels.
The three tiers of arcades are faced by three-quarter columns and entablatures, Doric in the first story, Ionic in the second, and Corinthian in the third. Above them is an attic story with Corinthian pilasters and small square window openings in alternate bays. At the top brackets and sockets carry the masts from which the velarium, a canopy for shade, was suspended.
The construction utilized a careful combination of types: concrete for the foundations, travertine for the piers and arcades, tufa infill between piers for the walls of the lower two levels, and brick-faced concrete used for the upper levels and for most of the vaults.
Coliseum still continues to inspire architects of the modern day, and virtually every modern sports stadium still bears the irresistible imprint of the Coliseum's original design. Until the 19th century, it remained the largest amphitheatre in the world.

Gladiators
In ancient Rome, class of professional fighters, who performed for exhibition. Gladiatorial combats usually took place in amphitheaters. They probably were introduced from Etruria and originally were funeral games. The gladiators were paired off to fight each other, usually to the number of about 100 couples, although in the imperial shows there were sometimes as many as 5,000 pairs. There were various types of gladiators, armed and armored differently. Thus a heavily armored man, a Mirmillo or Samnite, might be opposed to a Retiarius, who fought almost naked, with a net and a trident as his only weapons. He also might be pitted against a Thracian, who fought with a dagger and a small round shield. Often gladiators were made to fight wild beasts. A defeated gladiator was usually killed by the victor unless the people expressed their desire that he be spared. At first, gladiators were invariably slaves or prisoners, including Christians. They normally underwent rigid training, and some gained immense popularity. Later, impoverished freedmen also sought a living as gladiators, and finally even members of the ruling classes took part in gladiatorial combats on an amateur basis. Constantine I forbade gladiatorial games, but they nonetheless continued until AD 405. Some gladiators, led by Spartacus , took part in the third of the Servile Wars.