The need of special buildings for the ludi gladiatori, the venationes and their machines, was felt rather late in the Roman world and in Rome even later than anywhere.

Dio Cassius called the amphitheater built by Iulius Caesar a sort of venatorius theatreand it's called amphitheatre as it is an amount of seats without the stage (C. Dio,XXXVI,58). For Vitruvius it means theatrum with tribunes all around.

The evolution of the amphitheatre, from a temporary and wooden unstable construction, to be a steady stone structure, happened in Regio I Campania where the ludi gladiatori involved and were held first. According to a letter by Strabo, in the ancient times, these kind of ludi were held also by the tombs, or in the Forum, or even during the funeral banquets (which confirm the funeral origin of the games).

Usually the walls and the structures of the amphitheatre were raised on a flat ground: for the Coliseum, the most famous amphitheater, was chosen Nero's garden pool. But we have other examples where the material was excavated from the center as from a quarry and used for the nearby structures. Sometime the quarry was excavated in a high ground so that supporting walls were not needed. Or, the amphitheatre leaned to a hill so to have a perimetrical wall reduced in its length.

The ellipse's dimensions vary between the greatest, the Coliseum (Amphiteatrum Flavium) with axis of 187 mts x 155 mts, and the shortest, in Ventimiglia, measuring only 35 mt x 31 mt.

Another feature of an amphitheather is the ratio between the max axis and the min one of the arena; it is a measure to realize how much the ellipse is "smashed". The more similar to a circle (1,05) was the one in Lucus Feroniae (by Capena, Italy), the most longish (2,09) the one in St.Bernarde de Comminges.