Timgad (called Thamugas or Tamugadi in old Berber) was a Roman colonial town in the Aurès Mountains of Algeria, founded by the Emperor Trajan around AD 100. The full name of the town was Colonia Marciana Ulpia Traiana Thamugadi. Trajan commemorated the city after his mother Marcia, father Marcus Ulpius Traianus and his eldest sister Ulpia Marciana. Located in modern-day Algeria, about 35 km east of the town of Batna, the ruins are noteworthy for representing one of the best extant examples of the grid plan as used in Roman city planning.
The city was founded ex nihilo as a military colony by the emperor Trajan around AD 100. It was intended to serve primarily as a bastion against the Berbers in the nearby Aures Mountains. It was originally populated largely by Parthian veterans of the Roman army who were granted lands in return for years of service. The city enjoyed a peaceful existence for the first several hundred years and became a center of Christian activity starting in the 3rd century, and a Donatist center in the 4th century. In the 5th century, the city was sacked by the Vandals before falling into decline. In AD 535 the Byzantine general Solomon found the city empty when he came to occupy it. In the following century, the city was briefly repopulated as a primarily Christian city before being sacked by Berbers in the 7th century and then abandoned.
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. The encroachment of the Sahara on the ruins was the principal reason why the town is so well preserved.
After the Berber sacking in the 7th century the city disappeared from history until its excavation in 1881.
Located at the intersection of six roads, the city was walled but not fortified. Originally designed for a population of around 15,000, the city quickly outgrew its original specifications and spilled beyond the orthogonal grid in a more loosely organized fashion. At the time of its founding, the area surrounding the city was a fertile agricultural area, about 1000 meters above sea level. The original Roman grid plan is magnificently visible in the orthogonal design, highlighted by the decumanus maximus (east-west-oriented street) and the cardo (north–south-oriented street) lined by a partially restored Corinthian colonnade. The cardo does not proceed completely through the town but instead terminates in a forum at the intersection with the decumanus.
At the west end of the decumanus rises a 12 m high triumphal arch, called the Arch of Trajan, which was partially restored in 1900. The arch is principally of sandstone, and is of the Corinthian order with three arches, the central one being 11′ wide. The arch is also known as the Timgad Arch. A 3,500-seat theater is in good condition and is used for contemporary productions. The other key buildings include four thermae, a library, and a basilica. The Capitoline Temple is dedicated to Jupiter and is of approximately the same dimensions as the Pantheon in Rome. Nearby the capitol is a square church with a circular apse dating from the 7th century AD. Southeast of the city is a large Byzantine citadel built in the later days of the city.