the largest of several forts in the area which follow the line of the Fossatum. In the 5th century there is still mention of a sector of the limes called Gemellensis just prior to the Vandal invasion. Other than that, the history of Gemellae after 253 AD remains uncertain. No Christian artefacts have been recovered, so there is no current archaeological evidence for a Byzantine presence. However, Justinian is known to have ordered Belisarius in 534 AD to restore the fortifications of the limes as they were before the Vandal invasion. The 6th-century historian Procopius mentions a Meleon as one of those forts rebuilt as a result, which may have been Gemellae. The 9th-century Arab historian Khalifa ibn Khayyat relates that when Abu al-Muhajir Dinar was emir of Ifriqiya (c. 675–682) he conquered Mila which may have been Gemellae. Gemellae has now been reclaimed by the desert, and excavators have complained about the continually blowing sand. The remains of the fort are known locally as al-Qasba (casbah, exactly a fort). Archaeology The great fort (praetorium or General Headquarters) of Gemellae is rectangular with sides oriented to the cardinal directions, constructed in a manner common to most Roman castra. It measures 150 m north to south and 190 m east to west. For the most part, the masonry wall was about 3 m thick, using stone from a quarry 14 km distant. However, the fort's corners were rounded and reinforced to a thickness of 4.85 m. Just outside the masonry wall was an earth wall (vallum). There was a gate in each side, and a number of towers. The towers were situated at each corner and at each gate, also the short sides of the fort had 2 additional ones and the long sides 3, i.e. one tower every 30 m, compared with one tower per 60 m at the Legion's headquarters at Lambaesis. The towers had no external bastions, interiorly they reduced the wall thickness by about 1.5 m. The interior courtyard was entirely paved over, and the walls and columns painted. The oldest layer of paint was a reddish purple, later covered by a cream base on which were painted various designs. The columns, for example, were painted with fruiting grapevines. Outside the fort, the town was surrounded by a vallum at a distance of 700–800 m from the centre of the praetorium. Just outside the fort was a