The Romano-Libyan farm Lm4 includes a ‘barrage’, water control walls and farm buildings. These were built as part of an agro-hydrological farm system at the confluence of the Wadi el Amud and the Wadi Umm el Bagul in the Libyan pre-desert. The farm appears to have functioned in a geomorphological environment not dissimilar to that which prevails today — with occasional rain storms producing overland flow and floods interrupting a dominance of aeolian processes. Field mapping revealed that substantial scatters of midden made up of abraded pottery, bone, and animal dung occur around the buildings. Animals appear to have been kept near to these buildings, which lead to coprolites becoming a very important component of these anthropogenic sediments. Such activity gave rise to significant bioturbation of the sediments, and a notable former vegetation cover. The petrology of the building stones used in the farm buildings is described using petrographic thin section studies. Cavernous weathering and case-hardening are shown to have developed after the stone was incorporated within the building. The size and distribution of these features are shown to relate to the nature of the bedrock used — especially the form and distribution of joints and sedimentary parting planes — as well as the distribution and thickness of the surficial soils and sediments, and the shape and form of the building.