§333. The Barriers.--The _carceres_ were the stations of the chariots and teams when ready for the races to begin. They were a series of vaulted chambers entirely separated from each other by solid walls, and closed behind by doors through which the chariots entered. The front of the chamber was formed by double doors, with the upper part made of grated bars, admitting the only light which it received. From this arrangement the name _carcer_ was derived. Each chamber was large enough to hold a chariot with its team, and as a team was composed sometimes of as many as seven horses the "prison" must have been nearly square. There was always a separate chamber for each chariot. Up to the time of Domitian the highest number of chariots was eight, but after his time as many as twelve sometimes entered the same race, and twelve _carceres_ had, therefore, to be provided, although four chariots was the usual number. Half of these chambers lay to the right, half to the left of the _porta pompae_. The appearance of a section of the _carceres_ is shown in Fig. 141.
[Illustration: FIGURE 142. BOX OF THE DATOR LUDORUM]
§334. It will be noticed from the plan (§330) that the _carceres_ were arranged in a curved line. This is supposed to have been drawn in such a way that every chariot, no matter which of the _carceres_ it happened to occupy, would have the same distance to travel in order to reach the beginning of the course proper at the nearer end of the _spina_. There was no advantage in position, therefore, at the start, and places were assigned by lot. In later times a starting line (_linea alba_) was drawn with chalk between the second _meta_ and the seats to the right, but the line of _carceres_ remained curved as of old. At the ends of the row of chambers, towers were built which seem to have been the stands for the musicians; over the _porta pompae_ was the box of the chief official of the games (_dator ludorum_), and between his box and the towers were seats for his friends and persons connected with the games. In Fig. 142 is shown a victor pausing before the box of the _dator_ to receive a prize before riding in triumph around the arena.
§335. The Spina and Metae.--The _spina_ divided the race course into two parts, making a minimum distance to be run. Its length was about two-thirds that of the arena, but it started only the width of the track from the _porta triumphalis_, leaving entirely free a much larger space at the end near the _porta pompae_. It was perfectly straight, but did not run precisely parallel to the rows of seats; at the end B in the exaggerated diagram (Fig. 143) the distance BC is somewhat greater than the distance AB, in order to allow more room at the starting line (_linea alba_, §334), where the chariots would be side by side, than further along the course, where they would be strung out. The _metae_, so named from their shape (§284), were pillars erected at the two ends of the _spina_ and architecturally a part of it, though there may have been a space between. In Republican times the _spina_ and the _metae_ must have been made of wood and movable, in order to give free space for the shows of wild beasts and the exhibitions of cavalry that were originally given in the circus. After the amphitheater was devised the circus came to be used for races exclusively and the _spina_ became permanent. It was built up, of most massive proportions, on foundations of indestructible concrete (§210 f.) and was adorned with magnificent works of art that must have entirely concealed horses and chariots when they passed to the other side of the arena.