Campus Martius, English Field of Mars,in ancient Rome, a floodplain of the Tiber River, the site of the altar of Mars and the temple of Apollo in the 5th century bc. Originally used primarily as a military exercise ground, it was later drained and, by the 1st century bc, became covered with large public buildings—baths, amphitheatre, theatres, gymnasium, crematorium, and many more temples. The Pantheon is the most notable structure extant. The historian Livy (1st century bc) called the area campus ignifer because of the volcanic smoke often seen there.
Rome: Campus Martius
The rest of the river bend northward was known as theCampus Martius (Field of Mars). Marshy in places, with a few temples
