these would have required full use of the Circus. On many other days, charioteers and jockeys would need to practise on its track. Otherwise, it would have made a convenient corral for the animals traded in the nearby Forum Boarium, just outside the starting gate. Beneath the outer stands, next to the Circus' multiple entrances, were workshops and shops. When no games were being held, the Circus at the time of Catullus (mid-1st century BC) was probably "a dusty open space with shops and booths ... a colourful crowded disreputable area" frequented by "prostitutes, jugglers, fortune tellers and low-class performing artists." Rome's emperors met the growing popular demand for regular ludi and the need for more specialised venues, as essential obligations of their office and cult. Over the several centuries of its development, the Circus Maximus became Rome's paramount specialist venue for chariot races. By the late 1st century AD, the Colosseum had been built to host most of the city's gladiator shows and smaller beast-hunts, and most track-athletes competed at the purpose-designed Stadium of Domitian, though long-distance foot races were still held at the Circus. Eventually, 135 days of the year were devoted to ludi. Even at the height of its development as a chariot-racing circuit, the circus remained the most suitable space in Rome for religious processions on a grand scale and was the most popular venue for large-scale venationes; in the late 3rd century, the emperor Probus laid on a spectacular Circus show in which beasts were hunted through a veritable forest of trees, on a specially built stage. With the advent of Christianity as the official religion of the Empire, ludi gradually fell out of favour. The last known beast-hunt at the Circus Maximus took place in 523, and the last known races there were held by Totila in 549. Topography and construction Regal era The Circus Maximus was sited on the level ground of the Valley of Murcia (Vallis Murcia), between Rome's Aventine and Palatine Hills. In Rome's early days, the valley would have been rich agricultural land, prone to flooding from the river Tiber and the stream which divided the valley. The stream was probably bridged at an early date, at the two points where the track had to cross it, and the earliest races would have been held within an agricultural landscape, "with nothing more than turning posts, banks where spectators could sit,