Only a single capital and a few fragments survive of the pilasters that decorated the interior of the cella of the Temple of Mars Ultor. They are based on the Corinthian order but, instead of scrolled volutes, the corners of the abacus are supported by protomes of Pegasus, the wings of which extend back to form elegant acanthus volutes. The horses, themselves, with stiff archaic manes, emerge from vine shoots covered with acanthus leaves that curl and terminate in rosettes. More acanthus leaves decorate the lower part of the capital.
Compare Pegasus to the winged creature that adorns the rhyton of Pontios, a large fountain in the shape of a drinking horn resting on a bed of curled water-lily leaves. Sometimes mistakenly identified as a Chimera, the figure shows a lion's head with the horns of a ram, the mane of a horse, and the feet of a bull.
Water issued below the figure and flowers possibly grew in the hollow mouth. Now in the Palazzo dei Conservatori (Capitoline Museums), the marble sculpture was discovered in 1874 on the Esquiline Hill in the extensive gardens of Gaius Maecenas, a patron of the arts and close friend of Augustus, who slept at his house whenever he was not well (Suetonius, Life of Augustus, LXXII.2). Dio comments that Maecenas was the first "to construct a swimming-pool of warm water in the city, and also the first to devise a system of symbols to give speed in writing" (Roman History, LV.7.6).
It was from a vantage point in the Horti Maecenatis that Nero viewed the burning of Rome (Suetonius, Life of Nero, XXXVIII.2; cf. Dio, LXII.18.1 "the roof of the palace," which Nero had connected to the gardens by the Domus Transitoria).
This example of a Pegasus protome is from the Hippodrome in Constantinople and possibly adorned the Kithisma, where the emperor sat to watch the races. Fittingly, "hippodrome" itself derives from the Greek for "horse" and "path" and was the venue for chariot racing. The capital dates to the first half of the sixth century AD and is in the Archaeological Museums of Istanbul.
Reference: The Museum of the Imperial Forums in Trajan's Market (2007) edited by Lucrezia Ungaro.
See also Chimera of Arezzo.