The archaeological complex of Sa Mandra Manna is located on a plateau about 3 km from Tula along an ancient path leading to the Roman and Byzantine castrum of Castro (Oschiri). It is a naturally defended place suitable for agriculture and animal husbandry: these are the reasons that probably prompted humans to settle in this area. A prehistoric bicellular hypogeum burial site with longitudinal development excavated in the southern wall of the plateau has been identified at the site, which has, in the upper part, a natural rock slab that, when viewed frontally, gives the monument a megalithic appearance; a small dolmen; a giants’ tomb; a spring; a megalithic wall with traces of later adaptations; and a corridor nuraghe. The megalithic wall, with a semicircular course, encircles part of the plateau. Constructed with a double row of polyhedral boulders, in some sections sub-rectangular, with a cavity filled with stones, the structure has an overall length of 120 meters and a maximum height of 3; there are also dolmen-type slabs. The wall of the corridor has boulders of considerable size, some of which have variously oriented linear incisions mostly vertical drawing lattice patterns. Small cup marks can be seen among the engravings. Although there are no precise iconographic comparisons so far, the context of the structure, its location, and the presence of cupmarks suggest that they are to be related to the megalithic time of occupation of the site.
