[Illustration: FIGURE 139. PLAN OF THE CIRCUS OF MAXENTIUS]
§330. Plan of the Circus.--All of the Roman circuses known to us had the same general arrangement, which will be readily understood from the plan of the Circus of Maxentius shown in Fig. 139. The long and comparatively narrow stretch of ground which formed the race course proper (_arena_) is almost surrounded by the tiers of seats, running in two long parallel lines uniting in a semicircle at one end. In the middle of this semicircle is a gate, marked _F_ in the plan, by which the victor left the circus when the race was over. It was called, therefore, the _porta triumphalis_. Opposite this gate at the other end of the arena was the station for the chariots (_AA_ in the plan), called _carceres_, "barriers," flanked by two towers at the corners (_II_), and divided into two equal sections by another gate (_B_), called the _porta pompae_, by which processions entered the circus. There are also gates (_HH_) between the towers and the seats. The exterior appearance of the towers and barriers, called together the _oppidum_, is shown in Fig. 140.
[Illustration: FIGURE 140. OPPIDUM OF A CIRCUS]
§331. The arena is divided for about two-thirds its length by a fence or wall (_MM_), called the _spina_, "backbone." At the end of this were fixed pillars (_LL_), called _metae_, marking the inner line of the course. Once around the _spina_ was a lap (_spatium_, _curriculum_), and the fixed number of laps, usually seven to a race, was called a _missus_. The last lap, however, had but one turn, that at the _meta prima_, the one nearest the _porta triumphalis_, the finish being a straightaway dash to the _calx_. This was a chalk line drawn on the arena far enough away from the second _meta_ to keep it from being obliterated by the hoofs of the horses as they made the turn, and far enough also from the _carceres_ to enable the driver to stop his team before dashing into them. The dotted line (_DN_) is the supposed location of the _calx_. It will be noticed that the important things about the developed circus are the _arena_, _carceres_, _spina_, _metae_, and the seats, all of which will be more particularly described.
§332. The Arena.--The arena is the level space surrounded by the seats and the barriers. The name was derived from the sand used to cover its surface to spare as much as possible the unshod feet of the horses. A glance at the plan will show that speed could not have been the important thing with the Romans that it is with us. The sand, the shortness of the stretches, and the sharp turns between them were all against great speed. The Roman found his excitement in the danger of the race. In every representation of the race course that has come down to us may be seen broken chariots, fallen horses, and drivers under wheels and hoofs. The distance was not a matter of close measurement either, but varied in the several circuses, the Circus Maximus being fully 300 feet longer than the Circus of Maxentius. All seem to have had constant, however, the number of laps, seven to the race, and this also goes to prove that the danger was the chief element in the popularity of the contests. The distance actually traversed in the Circus of Maxentius may be very closely estimated. The length of the _spina_ is about 950 feet. If we allow fifty feet for the turn at each _meta_, each lap makes a distance of 2,000 feet, and six laps, 12,000 feet. The seventh lap had but one turn in it, but the final stretch to the _calx_ made it perhaps 300 feet longer than one of the others, say 2,300 feet. This gives a total of 14,300 feet for the whole _missus_, or about 2.7 miles. Jordan calculates the _missus_ of the Circus Maximus at 8.4 kilometers, which would be about 5.2 miles, but he seems to have taken the whole length of the arena into account, instead of that merely of the _spina_.