The Roman town now known as Timgad was founded in A.D. 100 on command of the emperor Trajan (reigned 98 117) and named Colonia Marciana Trajana Thamugas for his sister. It was built on a high plateau north of the Aures Mountains in Algeria (then Numidia), 94 miles (150 kilometers) south of the modern town of Constantine. The Third Augusta Legion, effectively the Roman police force in North Africa, was garrisoned nearby, and Timgad, designed for veterans, was the archetypal Roman colony. The regular well-ordered layout became one of the principal sources of city plans in Europe and the New World from the fifteenth century until the beginning of the twentieth. It is therefore significant in the development of Western architecture and urban design. In turn, the inspiration for Timgad comes from the Roman army encampment, the castrum.
Perhaps because it was easy to set out, or perhaps because it suited military purposes, the right-angled grid formed the structure of the castrum, which might have served as a garrison for months or even years during a campaign. Two main streets, the Via Principia and the Via Praetoria, intersected at the legions command post. Both extended through fortified gates beyond the enclosing ditch and palisade. Many permanent towns later grew from a castrum; for example, most English cities with chester