Rome reached its peak ancient population when, in the second century CE, it supported as many as one million inhabitants – a number twice that of even the largest rival city in the Mediterranean. This statistic is impressive in itself, but it is also important as a striking illustration of the unique nature of the city within the Roman Empire, where no other city even came close in total population. Rome's privileged position was due primarily to one factor: it was home to the emperor, who controlled activities in the city either directly or through the appointed prefects and other officials who by the Antonine period had supplanted the traditional senatorial magistrates responsible for the maintenance of the urban fabric and its inhabitants (Hammond 1959: 444–6). The emperor's influence on the population and the physical structure of the city can hardly be overestimated – nor can the extent to which the monuments of the capital are able in turn to illuminate the character of the ruler: the intense familial piety of Antoninus Pius, the restraint of Marcus Aurelius, the insanity of Commodus and, most interestingly of all, the mysterious character of Hadrian.