When the first Roman Emperor, Augustus (reigned 27 BC – 14 AD), transformed the Roman Republic into the Roman Empire in 27 BC, he reformed the office of Prefect at the suggestion of his minister and friend Maecenas. Again elevated into a magistracy, Augustus granted the "praefectus urbi" all the powers needed to maintain order within the city. The office's powers also extended beyond Rome itself to the ports of Ostia and the Portus Romanus, as well as a zone of one hundred Roman miles (c. 140 km) around the city. The Prefect's office was called the "secretarium tellurense" (secretariat of Tellus). The find-spots of inscriptions honouring Prefects suggest that it was located on the Oppian Hill, near the Baths of Trajan. Acting as a quasi-mayor of Rome, the Prefect was the superintendent of all guilds and corporations ("collegia"), held the responsibility (via the "praefectus annonae") of the city's provision with grain from overseas, the oversight of the officials responsible for the drainage of the Tiber and the maintenance of the city's sewers and water supply system, as well as its monuments. The provisioning of the city's large population with the grain dole was especially important; when the Prefect failed to secure adequate supplies, riots often broke out.