Sulcus primigenius

The sulcus primigenius (Latin for "initial furrow") was the ancient Roman ritual of plowing the boundary of a new city—particularly formal colonies—prior to distributing its lots or erecting its walls. The Romans considered the ritual extremely ancient, believing their own founder Romulus had introduced it from the Etruscans, who had also fortified most of their cities. The ritual had the function of rendering the course of the city wall sacrosanct but, owing to the necessity of some profane traffic such as the removal of corpses to graveyards, the city gates were left exempted from the ritual.