The Great Wall of Syria

In the Bronze Age Syrian farmers in the plain feared barbarian herders from the mountains and took action to defend themselves, analysis of aerial photography and sites on the ground has revealed.

[A] fortified surveillance network over the territory dating from the second millennium (-2,000 to -1,550). It is the first time that such an extensive fortified system has been discovered in the territory. 

This structure, exceptional in its extent and designed to protect urban areas and their hinterlands, is composed of a series of fortresses, small forts, towers, and enclosures that run along the mountainous ridge which dominates the steppes of central Syria. The researchers' work suggests that the fortresses were made from large blocks on unsculpted basalt and formed walls several meters wide and high. In addition, each fortified site was positioned in such a way to ensure that it could see and be seen by others. The spatial organization of this network thus depended on the ability to communicate through light (or smoke) signals in order to rapidly convey information to the major centers of power. The purpose of this regional network would have been to defend the territory, to surveil and protect transport corridors and, above all, to protect the most attractive lands. 

These results consolidate field observations conducted prior to the exploration. These had already enabled the sites to be dated using ceramics collected on site. The access to aerial and satellite observations, from 1960 to the present day, made it possible to reconstruct the network beyond the limits of the zone under exploration. It has thus been identified across a north-south distance of around 150 km.

From Science Daily.

The parallel to the Great Wall of China is obvious. Before the wall was built, China has a similar visual relay.

Another system of similar forts is the source of Britain's "ley lines". Spain also had such a system.

Fantasy fans will also note the similarity to the "Warning beacons of Gondor."