The forum was placed more or less centrally, where the main north-south street met the main east-west street. The square (50 x 43 m) was surrounded by shops, a public lavatory, the judicial basilica, a temple dedicated to Trajan and his military victories and, in the north-east corner, the so-called Maison des Jardinières.

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.