Construction and design
The Stadium of Domitian was dedicated in AD 86, as part of an Imperial building programme at the Field of Mars, following the damage or destruction of most of its buildings by fire in AD 79. It was Rome's first permanent venue for competitive athletics. It was patterned after the Greek model and seated approximately 15,000 - 20,000 – a smaller, more appropriate venue for foot-races than the Circus Maximus. The substructures and support frames were made of brick and concrete – a robust, fire-retardant and relatively cheap material – clad in marble. Stylistically, the Stadium facades would have resembled those of the Colosseum; its floor plan followed the same elongated, U-shape as the Circus Maximus, though on a much smaller scale. Various modern estimates judge the arena length at approximately 200 – 250 metres, the height of its outer perimeter benches at 30 m (100 ft) above ground level and its inner perimeter benches at 4.5 m (15 ft) above the arena floor. This arrangement offered a clear view from most seats. The typically Greek layout gave the Stadium its Latinised Greek name, in agones (the place or site of the competitions). The flattened end was sealed by two vertically staggered entrance galleries and the perimeter was arcaded beneath the seating levels, with travertine pilasters between its cavea (enclosures). The formation of a continuous arena trackway by a raised "spina" or strip has been conjectured.
The Stadium of Domitian was the northernmost of an impressive series of public buildings on the Campus Martius. To its south stood the smaller and more intimate Odeon of Domitian, used for recitals, song and orations. The southernmost end of the Campus was dominated by the Theater of Pompey, restored by Domitian during the same rebuilding program.
The Stadium was used almost entirely for athletic contests. For "a few years", following fire-damage to the Colosseum in AD 217, it was used for gladiator shows. According to the Historia Augusta's garish account of Emperor Elagabalus, the arcades were used as brothels and the emperor Severus Alexander funded his restoration of the Stadium partly with tax-revenue from the latter. In Christian martyr-legend, St Agnes was put to death there during the reign of the emperor Diocletian, in or near one of its arcades. With the economic and political crises of the later Imperial and post-Imperial eras, the Stadium seems to have fallen out of its former use; the arcades provided living quarters for the poor and the arena a meeting place. It may have been densely populated: "With the decline of the city after the barbarian invasions, the rapidly dwindling population gradually abandoned the surrounding hills and was concentrated in the campus Martius, which contained the main part of Rome until the new developments in the nineteenth century." Substantial portions of the structure survived into the Renaissance era, when they were mined and robbed for building materials.
The Piazza Navona sits over the interior arena of the Stadium. The sweep of buildings that embrace the Piazza incorporates the Stadium's original lower arcades. They include the most recent rebuilding of the Church of Sant'Agnese in Agone, first founded in the ninth century at the traditional place of St. Agnes' martyrdom.