Here we see a mosaic portraying a race of four-horse chariots (the most common form of chariot race), which takes place in a typical circus (not necessarily the Circus Maximus). The figure in the lower right corner is lashing the horses as they speed by, while the man in the upper left corner is waiting to sprinkle water on the hot chariot wheels. The two men on horseback are probably pacesetters. Two bad accidents have occurred (lower left corner and upper right), always an attraction for the spectators.
At either end of the spina (here divided into two sections) are three metae, cone-shaped turning posts with an egg-like protuberance at the top (about which, more later). Between the two sections of the spina are two officials holding a palm branch and a wreath for the victor. Immediately to the left of these officials is an obelisk. At the eastern end of the spina of the Circus Maximus, there was an obelisk, which had been brought to Rome by Augustus in 10 BC from Heliopolis ("the Sun's city") to remind his fellow Romans of his great military victory over Antony and Cleopatra. Click here to see this obelisk, which is now in the Piazza del Popolo. There was another obelisk in the center of the spina that Constantine in 330 AD had originally planned to set up in Constantinople, but only got so far as the port city of Alexandria. Thirty-seven years later, his son Constantine II brought it along when he visited Rome. It is now located in the Piazza S. Giovanni in Laterano. The apparent connection between the obelisk and the chariot racing is that the obelisk was a symbol of Egyptian sun worship and in Greco-Roman myth, the sun is thought to ride in a horse-drawn chariot across the sky. Also, by a false etymology, the Circus was associated with Circe, the daughter of the Sun and the mother of Latinus, the eponymous king of the Latins in Italy.
In both sections of the spina are two wooden frames, one with eggs
on sticks, and the other with dolphins (not clear in this image) spewing
water. Both of these devices are lap counters. The seven eggs
and seven dolphins represent the seven laps of a chariot race. The
eggs are raised by an attendant as each lap is completed. The dolphins
are on a pivot so that their tail can be in either an up or down position.
It is not known why there are two apparently redundant lap-counting devices.
On the other hand, the symbolism of these devices is clear. The eggs
(along with the eggs on top of the metae) recall Castor and Pollux,
born from an egg, laid by their mother Leda, who was impregnated by Jupiter
in the form of a swan. The connection with horses lies in the fact
that Castor and Pollux were patrons of horsemen and also the the equestrian
order, whose name was derived from the word for horsemen (equites).
The dolphins seem to have been a later addition and were considered appropriate
to chariot racing because of their speed and connection with Neptune, the
god of water and horses.