Augustus instituted reforms aimed at increasing the safety of buildings in the city of Rome. Because of the dangers of fire and collapse, the height of the "insulae" were restricted by Augustus to 70 Roman feet called the "pes" (20.7 m), and again to an unspecified amount by Emperor Nero after The Great Fire of Rome in 64 AD. Emperor Trajan reduced the height to 60 Roman feet (17.75 m). According to the 4th-century Regionary catalogues, there were about 42,000–46,000 "insulae" in the city, as compared to about 1,790 "domūs" in the late 3rd century. Data on the number of "insulae" and to a lesser extent "domūs" are used for classical demography. The city's population in the late 3rd century is thought to have fluctuated between 700,000–800,000, down from more than 1 million, based also on figures for the amount of grain required to feed the population in Rome and surrounding areas.