The foregoing account of the Athenian theater is founded, in the main, upon Dörpfeld’s conclusions, but the reader needs to be warned that not all of his conclusions are acceptable to everyone. Until about half a century ago our information concerning Greek theaters was largely restricted to literary tradition. There was no theater of the earlier Greek types above ground, and even the exact location of the Athenian theater had been, during many centuries, forgotten. The literary tradition was mainly derived from Vitruvius, a Roman architect at the beginning of the Christian era, who devoted two chapters of Book V in his work _On Architecture_ to a description of Greek and Roman theaters. According to him, the front and back walls of the Roman stage were determined by the diameter of the orchestral circle and one side of an inscribed equilateral triangle; in other words, its depth would be one-half the radius of the orchestra (Fig. 42).[158] Its height was not to exceed five feet,[159] since all the performers stood on the stage and the unelevated front half of the orchestral circle was reserved for the seats of senators. In the Greek theater, on the other hand, Vitruvius asserted that the front wall of the stage was marked by one side of an inscribed square, and its back wall, which he calls the _scaenae frons_, by the parallel tangent, its depth being thus about three-tenths of the radius (Fig. 43).[160] Its height was to range between ten and twelve feet. Vitruvius expressly states that this stage in the Greek theater was called a logium, that the tragic and comic actors performed _in scaena_[161] and the “other artists” _per orchestram_, and that for this reason the Greeks drew a distinction between the adjectives “scenic” and “thymelic” as applied to performances and performers.[162] The differences between the two types of structure are obvious: (1) the auditorium and orchestra in Vitruvius’ Roman theater occupied exactly a semicircumference, in his Greek theater distinctly more than this; (2) the Roman stage was deep and low, the Greek high and comparatively shallow; (3) in the Greek theater both orchestra and stage were employed (separately) by different forms of entertainment; in the Roman theater all performers stood on the stage and the semicircular orchestra was occupied by the seats of senators.