See Salmasius ad Suetonius in Claudius c. 21. A twenty-fifth race, or missus, was added, to complete the number of one hundred chariots, four of which, the four colours, started each heat.
Centum quadrijugos agitabo ad flumina currus.
It appears that they ran five or seven times round the Meta (Suetonius in Domitian c. 4), and (from the measure of the Circus Maximus at Rome, the Hippodrome at Constantinople, etc.) it might be about a four-mile course.