8. The hill called Jani'culum, on the north bank of the Tiber, was fortified as an outwork by Ancus Martius, and joined to the city by the bridge; he also dug a trench round the newly erected buildings, for their greater security, and called it the ditch of the Quirites. 9. The public works erected by the kings were of stupendous magnitude, but the private buildings were wretched, the streets narrow, and the houses mean. It was not until after the burning of the city by the Gauls that the city was laid out on a better plan; after the Punic wars wealth flowed in abundantly, and private persons began to erect magnificent mansions. From the period of the conquest of Asia until the reign of Augustus, the city daily augmented its splendour, but so much was added by that emperor, that he boasted that "he found Rome a city of brick, and left it a city of marble." 10. The circumference of the city has been variously estimated, some writers including in their computation a part of the suburbs; according to Pliny it was near twenty miles round the walls. In consequence of this great extent the city had more than thirty gates, of which the most remarkable were the Carmental, the Esquiline, the Triumphal, the Naval, and those called Tergem'ina and Cape'na. 11. The division of the city into four tribes continued until the reign of Augustus; a new arrangement was made by the emperor, who divided Rome into fourteen wards, or regions.[9] The magnificent public and private buildings in a city so extensive and wealthy were very numerous, and a bare catalogue of them would fill a volume;[10] our attention must be confined to those which possessed some historical importance.