Mars (Latin: Mārs, adjectives Martius and Martialis) was the Roman god of war and also an agricultural guardian, a combination characteristic of early Rome. He was second in importance only to Jupiter, and he was the most prominent of the military gods worshipped by the Roman legions. His festivals were held in March, the month named for him (Latin Martius), and in October, which began and ended the season for military campaigning and farming.

Under the influence of Greek culture, Mars was identified with the Greek god Ares, whose myths were reinterpreted in Roman literature and art under the name of Mars. But the character and dignity of Mars differed in fundamental ways from that of his Greek counterpart, who is often treated with contempt and revulsion in Greek literature. Mars was a part of the Archaic Triad along with Jupiter and Quirinus, the latter of whom as a guardian of the Roman people had no Greek equivalent. Mars' altar in the Campus Martius, the area of Rome that took its name from him, was supposed to have been dedicated by Numa himself, the peace-loving semi-legendary second king of Rome. Although the center of Mars' worship was originally located outside the pomerium, or sacred boundary of Rome, Augustus brought the god into the center of Roman religion by establishing the Temple of Mars Ultor in his new forum.