The city, which was not built in a manner suitable to the grandeur of the empire, and was liable to inundations of the Tiber, 1 as well as to fires, was so much improved under his administration, that he boasted, not without reason, that he "found it of brick, but left it of marble." 2 He also rendered it secure for the time to come against such disasters, as far as could be effected by human foresight. A great number of public buildings were erected by him, the most considerable of which were a forum, 3 containing the temple of Mars the Avenger, the temple of Apollo on the Palatine hill, and the temple of Jupiter Tonans in the capitol. The reason of his building a new forum was the vast increase in the population, and the number of causes to be tried in the courts, for which, the two already existing not affording sufficient space, it was thought necessary to have a third. It was therefore opened for public use before the temple of Mars was completely finished; and a law was passed, that causes should be tried, and judges chosen by lot, in that place. The temple of Mars was built in fulfilment of a vow made during the war of Philippi, undertaken by him to avenge his father's murder. He ordained that the senate should always assemble there when they met to deliberate respecting wars and triumphs; that thence should be despatched all those who were sent into the provinces in the command of armies; and that in it those who returned victorious from the wars, should lodge the trophies of their triumphs. He erected the temple of Apollo4 in that part of his house on the Palatine hill which had been struck with lightning, and which, on that account, the soothsayers declared the God to have chosen. He added porticos to it, with a library of Latin and Greek authors; 5 and when advanced in years, used frequently there to hold the senate, and examine the rolls of the judges.
He dedicated the temple to Jupiter Tonans [or. Apollo Tonans],6 in acknowledgment of his escape from a great danger in his Cantabrian expedition; when, as he was travelling in the night, his litter was struck by lightning, which killed the slave who carried a torch before him. He likewise constructed some public buildings in the name of others; for instance, his grandsons, his wife, and sister. Thus he built the portico and basilica of Lucius and Caius, and the porticos of Livia and Octavia.7 and the theatre of Marcellus.8 He also often exhorted other persons of rank to embellish the city by new buildings, or repairing and improving the old, according to their means. In consequence of this recommendation, many were raised; such as the temple of Hercules and the Muses, by Marcius Philippus; a temple of Diana by Lucius Cornificius; the Court of Freedom by Asinius Pollio; a temple of Saturn by Munatius Plancus; a theatre by Cornelius Balbus9; an amphitheatre by Statilius Taurus, and several other noble edifices by Marcus Agrippa.10