Radiocarbon puts a defensive earthwork at Oued Beht in the second millennium BC

Dating an earthwork means dating something that sits beside it. The Oued Beht chronology comes from radiocarbon on deposits associated with the ditch, rampart and wall ^[5], so the construction date holds to the degree those deposits are stratigraphically tied to the building. The structure is described as multiphase ^[4]. That means more than one episode of digging and raising, and a date from one episode dates that episode.

What the new dates do most clearly is separate two occupations of one ridge. The project's earlier work put a farming and craft complex here at roughly 5,400 to 4,900 years ago ^[7], with polished stone axes in the thousands and finely made painted pottery ^[10]. The wall comes in at 4,000 to 3,500 years ago ^[3]. Take the youngest date in the first range and the oldest in the second and at least 900 years lie between them ^[1], so the earthwork belongs to a later use of the ridge than the dated agricultural complex.

Counting back from the mid-20th-century radiocarbon datum, that places the build at roughly 2050 to 1550 BC ^[2]. The authors call it the earliest confirmed defensive construction in North Africa outside Egypt ^[6].

The word "defensive" comes from the plan of the earthwork. A ditch, a rampart and a wall thrown across the narrow neck of a spur, with the fourth side closed by the natural scarp, is what the French archaeologist Armand Ruhlmann recorded in the 1930s and called a barred spur, or eperon barre ^[12]. The excavation does not identify a threat. The structures "likely relate to increasing competition over land, resources and possibly control of movement through the landscape," the excavators wrote ^[13], and it is not known exactly what they were built to counter ^[14].

The wider claim in the write-up is that second-millennium BC communities in northwestern Africa were shaping their environment and engaging in networks of interaction across the Mediterranean world ^[17]. The evidence set out for the site's own economy is local: barley and wheat, wild plants, livestock ^[9], axes and pottery ^[10], and no imported object is named. On this material the earthwork supports the authors' statement about organization and structure in the Maghreb ^[15] more than it measures what moved in or out. The comparison the authors draw is with Iberia and Athens, regions where the later prehistoric record has been less fragmentary than the Maghreb's ^[18].

The same defensive line was rebuilt in the 11th to 13th centuries AD ^[16], between about 2,500 and 3,300 years after it first went up ^[3]. Whether prehistoric Oued Beht was a permanent village, a seasonal center or something else is still open ^[11].