Abstract Two representative samples of mortar from Roman water supplies systems unearthed in an archaeological site in North Africa and dated to around the first century AD have been studied. Both samples were found to have a lime-based binder medium and aggregates composed of pottery sherds and pozzolana. Permeability to water of the two mortars varies significantly and can be correlated with the pore microstructure of the constituent phases, determined using the mercury intrusion technique.