Limes Arabicus

The Limes Arabicus was a desert frontier of the Roman Empire, in the province of Arabia Petraea. It ran -at its biggest extension- for about 1,500 km, from Northern Syria to Southern Palestine and northern Arabia, forming part of the wider Roman limes system. It had several forts and watchtowers.

Purpose
The reason of this defensive "Limes" was to protect the Roman "Province of Arabia" from attacks of the barbarian tribes of the Arabian desert.

"For more than five centuries the Limes Arabicus guarded the southeastern frontier of the Roman Empire"

Next to the limes arabicus Trajan built a major road, the Via Nova Traiana, from Bostra to Aila on the Red Sea, a distance of 267 miles. Built between 111 and 114 AD, its primary purpose may have been to provide efficient transportation for troop movements and government officials as well as facilitating and protecting trade caravans emerging from the Arabian peninsula. It was completed under Hadrian.

During the Severan dynasty (AD 193-235), the Romans strengthened their defenses on the Arabian frontier. They constructed several forts at the northwest end of the Wadi Sirhan, and they repaired and improved roads. One was the important Qasr Azraq.

"A larger fort is Humeima (ancient Auara), which was built in the late second century and is therefore the earliest known Roman fort on the Arabian frontier. It was located on the Via Nova between Petra (44 km, 27 mi., to the north) and Aila (55 km, 34 mi., to the south) in the Hisma, Jordan's southern desert. The fortress was built at the north edge of a major Nabataean, Roman, and Byzantine community. It was probably abandoned in the fourth century. It is about 3 ha. (more than 7 acres) in size and rectangular in shape. It had four gates, one in the middle of each wall. It had projecting rectangular interval and corner towers. It could have housed a standard auxiliary unit of 500 men."

Around 300 AD, Diocletian partitioned the old province of Arabia by transferring the southern region to the province of Palestine. Later in the 4th century, the southern region was detached from Palestine as a separate province, which eventually was called Palaestina Tertia. Each province was administered by a praeses with civil authority and a dux with military authority.

Diocletian engaged in a major military expansion in the region, building a number of forts (castella), watchtowers, and fortresses along the fringe of the desert just east of the Via Nova. The term used for this north-to-south line of military installations is limes Arabicus, which means "Arabian frontier." This line of defense extended from south of Damascus to Wadi al-Hasa. The region from Wadi Mujib to Wadi al-Hasa contained four castella and a legionary camp.

The frontier zone south of Wadi al-Hasa may have been called the "Limes Palaestina", which extended to the Red Sea at Aila (Aqaba). In this region, ten castella and a legionary camp have been identified. The exact meaning of the name is unclear, as it 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 describe the region under the military control of the dux Palaestinae, the military governor of the Palaestinian provinces.

There were Roman castra every one hundred km with the purpose to create a line of protection and control: in the south there 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 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 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 4th or early 5th century.

End
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. The main purpose of the Limes Arabicus is disputed; it may have been used both to defend from Saracen raids and to protect the commercial lines from desert-based robbers.

After the Arab conquest the Limes arabicus was left to disappear (but some fortifications were used and reinforced in the following centuries).