of the track, barring the starting gates and a processional entrance at the semi-circular end. The track measured approximately 621 m (2,037 ft) in length and 150 m (387 ft) in breadth. A canal between the track perimeter and its seating protected spectators and help drain the track. The inner third of the seating formed a trackside cavea. Its front sections along the central straight were reserved for senators, and those immediately behind for equites. The outer tiers, two thirds of the total, were meant for Roman plebs and non-citizens. They were timber-built, with wooden-framed service buildings, shops and entrance-ways beneath. The total number of seats is uncertain, but was probably in the order of 150,000; Pliny the Elder's estimate of 250,000 seating places is unlikely. The wooden bleachers were damaged in a fire of 31 BC, either during or after construction. Imperial era The fire damage of 31 was probably repaired by Augustus (Caesar's successor and Rome's first emperor). He modestly claimed credit only for an obelisk and pulvinar at the site but both were major projects. Ever since its quarrying, long before Rome existed, the obelisk had been sacred to Egyptian Sun-gods. Augustus had it brought from Heliopolis at enormous expense, and erected midway along the dividing barrier of the Circus. It was Rome's first obelisk, an exotically sacred object and a permanent reminder of Augustus' victory over his Roman foes and their Egyptian allies in the recent civil wars. Thanks to him, Rome had secured both a lasting peace and a new Egyptian Province. The pulvinar was built on monumental scale, a shrine or temple (aedes) raised high above the trackside seats. Sometimes, while games were in progress, Augustus watched from there, alongside the gods. Occasionally, his family would join him there. This is the Circus described by Dionysius of Halicarnassus as "one of the most beautiful and admirable structures in Rome", with "entrances and ascents for the spectators at every shop, so that the countless thousands of people may enter and depart without inconvenience." The site remained prone to flooding, probably through the starting gates, until Claudius made improvements there; they probably included an extramural anti-flooding embankment. Fires in the crowded, wooden perimeter workshops and bleachers were a far greater danger. A fire of 36 AD seems to have started in a basket-maker's workshop under the stands, on the Aventine side; the emperor Tiberius compensated various