Timgad, located to the north of the slope of the Aurès in a mountainous site of great beauty, 480 km south-east of Algiers and 110 km to the south of Constantine, is a consummate example of a Roman military colony created ex nihilo. It illustrates a living image of Roman colonisation in North Africa over three centuries. The Colonia Marciana Traiana Thamugadi was founded in AD 100 by Emperor Trajan, probably as an encampment for the 3rd Augustan Legion which, thereafter, was quartered at Lambaesis. Its model town-planning and its particular type of civil and military architecture reflects an important interchange of ideas, technologies and traditions exercised by the central power of Rome on the colonisation of the high plains of Antique Algeria.
Timgad adopts the guidelines of Roman town-planning governed by a remarkable grid system. With its square enclosure and orthogonal design based on the cardo and decumanus, the two perpendicular routes running through the city, it is an excellent illustration of Roman urban planning laid out with great precision. By the middle of the 2nd century, the rapid growth of the city had ruptured the narrow confines of its original foundation. Timgad spread beyond the perimeters of its ramparts and several major public buildings are built in the new quarters: Capitolium, temples, markets and baths. Most of these buildings date from the Severan period when the city enjoyed its Golden Age, also attested by immense private residences.
A strong and prosperous colony, Timgad must have served as a compelling image of the grandeur of Rome on Numidian soil. Timgad possesses a rich architectural inventory comprising numerous and diversified typologies, relating to the different historical stages of its construction: the defensive system, buildings for the public conveniences and spectacles, and a religious complex. Buildings, constructed entirely of stone, were frequently restored during the course of the Empire: the Trajan Arch in the middle of the 2nd century, the Eastern gate in 146, and the Western gate under Marcus-Aurelius. The streets were paved with large rectangular limestone slabs and, as attested by the 14 baths which still may be seen today, particular attention was paid to the disposition of public conveniences. The houses, of varying sizes, dazzle by their sumptuous mosaics, which were intended to offset the absence of precious marbles.
During the Christian period, Timgad was a renowned bishopric. After the Vandal invasion of 430, Timgad was destroyed at the end of the 5th century by montagnards of the Aurès. The Byzantine Reconquest revived some activities in the city, defended by a fortress built to the south, in 539, reusing blocks removed from Roman monuments. The Arab invasion brought about the final ruin of Thamugadi which ceased to be inhabited after the 8th century.