Vitruvius' theory of optical adjustment is based on the hypothesis that one sees the architectural order from a certain distance. This distance, which can be found out by a simple calculation, is about 60 feet and 120 feet. It is significant that these scales correspond to those of the inner space of the basilica that Vitruvius designed. In the academic discussions of the 17th and 18th century, his theory was sometimes approved and sometimes denied, but this ideal scale of space revived in its practical discussions.