Etruscan tomb paintings of chariot races offer a possible seating model for this earliest phase; noble sponsors and other dignitaries sit in elevated stands, complete with awning. Commoners lounge or sit below, at ground level. At the early Circus Maximus, the sloping ground afforded the possibility of turf seating tiers at an early date – as imagined by Ovid in his account of the first Consualia – replaced with wooden seating tiers by later sponsors and benefactors. See Humphrey 1986, pp. 65–66, 68–69, for early metae and a possible canal as central dividing barrier, see summary on pp. 292–3. Humphrey, John H. (1986). Roman Circuses: Arenas for Chariot Racing. University of California Press. ISBN978-0-520-04921-5.
Humphrey 1986, p. 171; the gates probably used the same animal-sinew torsion springing as the Roman ballista; Ibid, pp. 137–138: opposing teams of Reds and Whites are prominent in late Republican literature, and Greens and Blues in the Imperial era. Some Roman authors held that team-racing in multiple colors dated back to the regal era. Ibid, p. 175 for allocation of stalls by lottery. Humphrey, John H. (1986). Roman Circuses: Arenas for Chariot Racing. University of California Press. ISBN978-0-520-04921-5.
As far as is known, there was no significant expansion of seating between Caesar's improvements and Pliny's estimate of 250,000 seats. His estimate ignores the necessary interruptions of seating rows by access stairways and corridors. It might represent a per foot run seating estimate, or include those watching from the nearby heights, outside the building proper. In late Imperial regionary catalogues, seating estimates for the Circus become even wilder; one gives an impossible 450,000 seats. Discussion is in Humphrey 1986, p. 126 Humphrey, John H. (1986). Roman Circuses: Arenas for Chariot Racing. University of California Press. ISBN978-0-520-04921-5.
Nero, inordinately fond of chariot-racing, may have considered the Circus rebuilding a priority but the overall cost of Rome's rebuilding must have proved an extraordinary drain on Imperial and public funds. Wooden bleachers for the Roman masses were an expedient, cost-effective solution. If Nero had grander plans for the Circus, they ended with his suicide under compulsion, after a coup d'etat in AD 68. Humphrey 1986, p. 101 Humphrey, John H. (1986). Roman Circuses: Arenas for Chariot Racing. University of California Press. ISBN978-0-520-04921-5.
Most modern sources use spina (a spine) for the central barrier, based on a single, very late Roman source (Cassiodorus), but most Roman sources used euripus, a Greek word meaning a channel, strait, or canal, and thus a barrier. See Humphrey 1986, p. 175 Humphrey, John H. (1986). Roman Circuses: Arenas for Chariot Racing. University of California Press. ISBN978-0-520-04921-5.
Humphrey 1986, pp. 61–62. For Murcia's shifting topographical associations, see Otto Skutsch, "Enniana IV: Condendae urbis auspicia", The Classical Quarterly, New Series, Vol. 11, No. 2 (Nov., 1961), pp. 252–67. Humphrey, John H. (1986). Roman Circuses: Arenas for Chariot Racing. University of California Press. ISBN978-0-520-04921-5.