Legionary Fortresses in Arabia
Rome's line of defense consisted of three or four legionary fortresses, which are located at intervals of about a hundred kilometers. The northernmost was in the capital of Bostra, which has not been excavated because much of it is located beneath the modern city. It was manned by the Legio III Cyrenaica from the second century until at least the turn of the fifth century. Today, it is located in southern Syria, 10 km (6 mi.) north of the Jordanian border. It is 16.8 ha (41.5 acres) in size and rectangular in shape. It may have been constructed soon after 106.
In the central region was el-Lejjun, which is called Betthorus in Roman writings. It was built around AD 300 and housed the Legio IV Martia. It is 4.6 ha (11.4 acres) in size and rectangular in shape. It had semicircular corner towers and twenty U-shaped interval towers. Each wall has a gate in its middle. Its original construction could house two thousand men. After an earthquake in AD 363 destroyed much of the fort, fewer barracks were rebuilt so that it housed only one thousand men.
el-Lejjun
Excavations have uncovered a bath, church, reservoir, two tribunals, and a horreum (grain storage building). It was damaged by another earthquake in AD 505 and was finally destroyed by an earthquake in AD 551.
El-Lejjun was excavated for five seasons between 1980 and 1989 by S. Thomas Parker.
Farther south was the legionary fortress of Udruh, which is located just east of Petra. It is similar to el-Lejjun in size (12 acres) and design. It probably housed the Legio IV Ferrata. Alistair Killick, who excavated the site, dates it to the early second century, but Parker suggests a date in the late third or early fourth century.
A legionary camp may have also existed at Aila (modern 'Aqaba), which has been excavated by Parker since 1994. The city was located at the north end of the Gulf of 'Aqaba where it was a center of sea traffic. Several land routes also intersected here. The Legio X Fretensis, originally stationed in Jerusalem, was transferred here to the terminus of the Via Nova. So far, a stone curtain wall and projecting tower have been identified, but it is uncertain whether they were part of the city wall of Aila or the fortress. The evidence suggests the fort was constructed in the late fourth or early fifth century.