For decades researchers working in the Negev Highlands and central Sinai have encountered an enigmatic type of low, rectangular structure situated on ridges or along desert trails. These structures average 16 meters in length and 4 meters in width. Although only half a meter in height, their profile can be seen from long distances in the desert landscape. Often their height is augmented with singular or multiple tumuli that appear to be later additions. Three such rectangular structures were recently excavated in the site of Ma'ale Zadok, located at the head of an Early Bronze Age pass leading from the Ramon Crater in the Negev Highlands, Israel. A tumulus inserted into the largest one contained a few human bones that had been quite disturbed. Offerings discovered beneath the floor included a red-burnished hole-mouth jar dated to the EBII period and a fruit pit. A copper pin found below a grave in the smallest structure excavated may date to the Chalcolithic period. The structures appear to have served as road markers in the Early Bronze Age along roads that cross the central Sinai from Egypt and through a central corridor in the Negev Highlands apparently leading toward the ancient copper mines in Faynan in the Arabah. None are found north of Ma'ale Tsafir (tentatively identified as the biblical Scorpions Pass) or south of the Nahal Neqarot region. They appear to cluster near water sources and above major passes. This paper will present the evidence obtained in recent excavations at Ma'ale Zadok and discuss the distribution and function of the structures, as well as their accompanying features.