The arena which was enclosed by a marble parapet measured something over 205 metres long by 33 metres broad. It ended in a semicircular sphendone which was separated from the actual running track by the stone starting line of which remains have been found. As, however, no trace has been discovered of the corresponding line at the other end, it is impossible to determine definitely the length of the course. It must have been approximately 177 metres. At either end of the starting line stood a stone pillar, and between these pillars stood four curious double-headed herms. Two of these have been found almost intact, and portions of the other two have also been found.[448] They consist of square pillars about 6 feet high, on which stand back to back two heads, one bearded, the other beardless, sometimes said to represent a youthful Apollo and a bearded Dionysus. The heads, which are of rude and unfinished workmanship, are probably second-century copies of early originals. The pillars are divided to the height of 3 feet by a narrow slit through which, it has been suggested, may have passed the rope used in starting the races. The position of these herms along the starting line reminds one, however, of the somewhat similar rows of pillars at Epidaurus and Priene. The pillars at Epidaurus, it will be remembered, had likewise grooves on either side, though these did not as at Athens extend right through the pillars. In view of this resemblance it seems probable that both grooves and slits served for fixing either a sort of starting gate or a barrier used to enclose the course when dangerous exhibitions, such as fights of wild beasts, took place. Such shows it is known were exhibited in the stadium. The Emperor Hadrian on one occasion presented 1000 wild animals for this purpose. It was probably to secure the safety of the spectators on such occasions that the seats surrounding the whole arena were raised on a marble basement nearly 6 feet high. Above this rose 46 rows of marble seats, capable of seating at least 50,000 spectators. At the point where the curve of the sphendone began on the northern side a vaulted passage led underneath the seats and through the hill into the valley beyond. This passage may have served originally like the secret entrance at Olympia for the entrance of officials and competitors. In its later and more elaborate form it was probably intended by Herodes for the introduction of wild beasts, like the similar vaults in Roman amphitheatres. The principal entrance was at the other end of the stadium, near the Ilissus, where, it seems, elaborate Propylaea were erected, while the whole effect was greatly enhanced by a marble Doric colonnade which crowned the hills above the upper seats of the sphendone.