Roman antiquity, was, according to Livy, that space of ground, both within and without the walls, which the augurs, at the first building of cities, solemnly consecrated, and on which no edifices were allowed to be raised. Plutarch gives this account of the ceremony of drawing the pomerium: "They dug a trench, and threw into it the first-fruits of all things, either good by custom, or necessary by nature; and every man taking a small turf of earth of the country from whence he came, they cast them in promiscuously. Then making this trench their centre, they defended the city in a circle round it. After this, the founder yoking a bull and a cow together, ploughed a deep furrow, with a brazen ploughshare, round the bounds. The attendants took care that all the clods fell inwards, i.e. toward the city. This furrow they called Pomerium, and built the wall upon it."—Plutarch, in this account, is to be Pomerium understood as speaking of Rome.

Pomoerium Proferre, signifies to extend or enlarge a city, which could not be done by any, but those who had taken away some part of an enemy's country in war. But this qualification was sometimes dispensed with. Pomerium is quaeque pone muria, "behind the walls."