The Écusson — "the shield" — is the colloquial name for the old centre of Nîmes, so called because the loop of the former city walls (now boulevards) gives the district a rough shield shape. Everything inside is walkable: the Arena at the south, the Maison Carrée toward the west, the cathedral in the middle, the Halles to the east.
Streets are narrow, mostly pedestrianised, and lined with the pale stone houses of southern France. Lose half a day wandering with no plan beyond stopping for coffee and looking at the architecture.