The Temple of Mars Ultor (Mars the Avenger) stands in the Forum of Augustus. The building of the temple was the result of a pledge that Octavian, the great-nephew of Julius Caesar, made at the Battle of Philippi in 42 BCE. After winning the battle, in which Brutus and Cassius, two of Caesar's assassins, were killed, Octavian deemed he had avenged the assassination of his adoptive father. The temple was inaugurated forty years later in 2 BCE.
The huge marble statue of Mars 'the Avenger', which stood in the temple was surrounded by the legionary standards that had been lost to the Parthians in 53 BCE, but which were later recovered by Augustus in a bloodless show of diplomacy. The temple was the ceremonial focus of military politics and foreign policy. Augustus decreed that the Senate should meet there when discussing wars. Military commanders when setting off for the provinces officially took their leave there and it was also the setting for the ceremony in which high-born Roman boys (around the age of 16) assumed the adult toga, thus becoming eligible for military service.
On the gable of the temple were statues of Mars (father of Romulus) in the centre, flanked by the goddess Venus (mother of Aeneas) and Fortuna, and Romulus balanced on the opposite side by Roma.
Most of the temple has been destroyed, but three fluted marble columns (18 metres high) have survived, thanks to the fact that they were once used as a support for the brick bell tower of Santa Maria Annunziata ai Monti,a small church which was built in the ruins. The church, which was known as the Annunziatina on account of its small size, belonged to a convent of Dominican nuns. Although both church and convent were knocked down in the 1920s, the church doorway, surmounted by a relief of the Annunciation, survives.
The porticoes on the long sides of the forum were intended as venues for courts of justice and were curved into the two great exedras. The central niche of each exedra was occupied on one side by a statuary group showing Aeneas, ancestor of the Julian family, fleeing Troy with his father and his son, and on the other by Romulus, founder of Rome.
In the centre of the forum stood a bronze four-horse chariot (quadriga), drawn by the emperor Augustus. It bore the inscription: PATER PATRIAE (Father of the Fatherland).