So how exactly did the Campus Martius become the Campus Martius, latin for “field of Mars”? This name for the plain north of the Capitoline Hill does not appear in the written sources until around the mid-first century B.C.E. Until then our sources simply call it, “the field” or campus, likely in much the same way that today we would tell friends we’re heading to the “mall.” Romans knew the location well, however, as it had been used for centuries as the gathering place for citizen soldiers heading off to war in the Spring and to lay down weapons in the Fall upon return from battle. It was perfect for this purpose as it was flat, open and most importantly, outside of the city walls. Because soldiers could not bring their arms within the city limits (the line was called the pomerium), the Campus was ideal for military gatherings. The historian Livy noted that the field had been used as a place to gather troops as early as the mid-fifth century B.C. In 458 B.C.E., Cincinnatus was urged to leave his plow and gather Rome’s citizens with weapons in the Campus. The assembled troops left from the field north of the city and defeated the Aequians. The eponymous reference to the Roman god of war in the name of a field used for military mustering makes sense. But the connections to Mars run deeper.
Bust of Cincinnatus
Livy thought that the field became associated with Mars when Rome’s last king, Tarquinius Superbus, was removed and his lands seized in 509 B.C. The property was then “consecrated to Mars and became the Campus Martius.” Because the lands were taken at harvest time, the crops growing there were cut down, but religious restrictions forbade their consumption so they were thrown into the Tiber along with trees growing on the property, leaving the lands “wholly untilled and barren for the god of war.” The grains and trees tossed into the river became stuck in the mud and, according to ancient writers, formed the Tiber Island at the south end of the Field of Mars. Mars was worshipped by the Romans as early as the 6th century B.C.E. and his image appeared on coins in the 3rd century B.C.E. Mars was the only god for whom a month, March, was clearly named on the old Roman calendar, and it was March 1 that began the New Year.
Section of the Fasti Praenestini (calendar of ancient Praeneste, south of Rome) showing month of March (“In this month, sacrifices are made to Mars, recognized as the god of war”) (Palazzo Massimo alle Terme (early 1st century C.E.)
To honor the god, horse races know as the Equirria were held in the Campus Martius in March. As the poet Ovid noted, “the day has kept the appropriate name of Equirria, derived from the races which the god himself beholds in his own plain [in campo].” The most famous horse race dedicated to Mars was held every October on the Ides in the Campus and was known as the “October Horse.” In this contest, two chariots, each pulled by two fast horses, raced through an unknown location in the Campus Martius. One of the winning horses was sacrificed to the war god with the head and tail removed and the latter taken to the Regia so that its blood would drip on the hearth.
Mosaic of charioteer from the Villa of Baccano, Rome (Palazzo Massimo alle Terme) (3rd century C.E.)
To seal the connection of the space with the war god, we must turn to another myth, that of the founding of Rome by its first king, Romulus. As early as 200 B.C., Roman writers told of the twins Romulus and Remus, whose mother Rhea Silvia was raped by the war god. Hidden by their mother from her uncle Amulius who was jealous of any potential political rivals, the twins were placed in a basket and sent down river. Suckled by a she-wolf, the boys ultimately had their revenge against their great uncle before having their own falling out, leaving Romulus the sole ruler and first king of Rome. It was Romulus who, according to Plutarch, named the first calendar month after his real father, Mars. Romulus met his demise on the very field dedicated to the war god. Probably toward the end of the third or the beginning of the second century B.C. the legend developed that Romulus died on July 7 while inspecting his troops in the center of the Campus Martius. Rome’s first king disappeared in a storm cloud and his apotheosis became associated with a holiday celebrated every July on the Campus Martius and known as the Nonae Capratinae. The location of the demise of Romulus was believed to have occurred in a swampy depression in the middle of the Campus Martius known as the Caprae Palus or Goat Marsh. This is the likely site of the later built Pantheon of Agrippa where Hadrian’s remarkable round structure now stands.
Altar from Ostia showing twins suckled by she wolf next to personification of Tiber River. Above is eagle of Zeus and adoptive father of the twins and his brother. (Palazzo Massimo alle Terme) (2nd century C.E.)
Notwithstanding the strong associations with Mars, the Campus Martius contained no temple to honor the war until the late 2nd century B.C. when the general Junius Brutus Calaicus financed the construction of one at the southern end of the field. A single altar to Mars may have existed somewhere in the middle of the field much earlier. According to Livy, chairs were set up by the altar for officials to use as they observed elections held in the Field of Mars. The lack of more temples to Mars in the Campus Martius while many other deities were honored there is curious, but perhaps it was felt that more were unnecessary. After all, as Ovid suggested the entire field was the domain of the god of war.
 See P. Jacobs and D. Conlin, Campus Martius – The Field of Mars in the Life of Ancient Rome (“Campus Martius”), 37.
 Campus Martius, 21.
 Livy 2.5.2.
 Plut. Publ. 8.2.
 Livy 2.5.3-4; Suet. Claud. 25; Plut. Publ. 8.3.
 Ov. Fast. 2.860.
 Campus Martius, 29.
 Plut. Numa 19.
 Campus Martius, 33.
 Livy 1.16.1. See Plut. Rom. 27; Ov. Fast. 2.475.
 See Campus Martius, 30.
 Livy 40.45.8.
 Ov. Fast. 2.859.