In this region, ten castella and a legionary camp have been identified. The term may have referred to a series of fortifications and roads in the northern Negev, running from Rafah on the Mediterranean to the Dead Sea, or to the region under the military control of the "dux Palaestinae", the military governor of the Palaestinian provinces. There were castra every with the purpose to create a line of protection and control: in the south there was the legionary fortress at Adrou (Udruh), just east of Petra. It probably housed the Legio VI Ferrata, which was moved from Lajjun (in modern-day Israel) by Diocletian. It is similar to Betthorus (al-Lajjun in modern-day Jordan) in size () and design, and is in the plain of Moab, south of Wadi Mujib . Alistair Killick, who excavated the site, dates it to the early 2nd century, but Parker suggests a date in the late 3rd or early 4th 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 centre of sea traffic. Several land routes also intersected here. 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 4th or early 5th century. Troops were progressively withdrawn from the "Limes Arabicus" in the first half of the 6th century and replaced with native Arab "foederati", chiefly the Ghassanids. After the Muslim Arab conquest, the "Limes Arabicus" was largely left to disappear, though some fortifications were used and reinforced in the following centuries. The "limes" was overrun in 611 during the war with the Sasanians.