With a capacity of 250000 seats, the
Circus Maximus was undoubtedly the biggest of Rome and even of the Empire. In the foreground the
carceres
where one used to give the starting signal of the race that lasted 7 rounds
of the running track. In the south-east a triumphal arch closed the track,
the
Arch of Vespasian and Titus, that appears at the top of the picture.

.
The second biggest circus in Rome was that of Caligula and Nero, built in the valley of Vatican.
We can see here a reconstitution

in a drawing.