Beyond the Timgad arch, to the right, lay the temple of the genius of the colony. ''Genio Coloniae Thamug," found on an inscription on an altar. It had an irregularly shaped court with a colonnade containing statues of a number of gods. In ancient Roman religion, the genius was the individual instance of a general divine nature that is present in every individual person, place or thing (Genius loci applied to places).

Founded by Trajan in AD 100 as a colony for army veterans, the Colonia Marciana Traiana Thamugadi, and built by soldiers stationed at Lambaesis. Although its plan is overwhelmingly military, there is little doubt that Thamugadi was intended to be a town, not a military base. Its square shape comprises a grid of 111 blocks, each 20 sq. m; most were subdivided into properties for the individual settlers, while a good number were given over to public buildings. Following a Byzantine period, it was sacked by the Berbers in the 7th century and abandoned. The encroachment of the Sahara on the ruins was ironically the principal reason why the town is so well preserved. Because no new settlements were founded on the site after the 7th century, the town was partially preserved under sand up to a depth of approximately one meter until it was excavated in 1881. Designated a World Heritage Site by UNESCO in 1982.