nst the attack of a
relieving army from any quarter. These continuous lines of
circumvallation and contravallation were used only in the days of small
armies and small fortresses, and both terms are now obsolete.

CIRCUS (Lat. _circus_, Gr. [Greek: kirkos] or [Greek: krikos], a ring or
circle; probably "circus" and "ring" are of the same origin), a space,
in the strict sense circular, but sometimes oval or even oblong,
intended for the exhibition of races and athletic contests generally.
The circus differs from the theatre inasmuch as the performance takes
place in a central circular space, not on a stage at one end of the
building.

1. _In Roman antiquities_ the circus was a building for the exhibition
of horse and chariot races and other amusements. It consisted of tiers
of seats running parallel with the sides of the course, and forming a
crescent round one of the ends. The other end was straight and at right
angles to the course, so that the plan of the whole had nearly the form
of an ellipse cut in half at its vertical axis. Along the transverse
axis ran a fence (_spina_) separating the return course from the
starting one. The straight end had no seats, but was occupied by the
stalls (_carceres_) where the chariots and horses were held in
readiness. This end constituted also the front of the building with the
main entrance. At each end of the course were three conical pillars
(_metae_) to mark its limits.

The oldest building of this kind in Rome was the _Circus Maximus_, in
the valley between the Palatine and Aventine hills, where, before the
erection of any permanent structure, races appear to have been held
beside the altar of the god Consus. The first building is assigned to
Tarquin the younger, but for a long time little seems to have been done
to complete its accommodation, since it is not till 329 B.C. that we
hear of stalls being erected for the chariots and horses. It was not in
fact till under the empire that the circus became a conspicuous public
resort. Caesar enlarged it to some extent, and also made a canal 10 ft.
broad between the lowest tier of seats (_podium_) and the course as a
precaution for the spectators' safety when exhibitions of fighting with
wild beasts, such as were afterwards confined to the amphitheatre, took
place. When these exhibitions were removed, and the canal (_euripus_)
was no longer necessary, Nero had it filled up. Augustus is said to have
placed an obelisk on the _sp