The microchemical and minero-petrographic characterisation of mortars used at Tharros (western Sardinia, Italy) for lining the walls of Phoenician-Punic cisterns has been carried out by means of the combined use of differential thermal analysis-thermogravimetry (DTA-TG), X-ray diffraction (XRD), scanning electron microscopy + energy dispersive spectrometry (SEM + EDS) and optical microscopy (OM). The microchemical and minero-petrographic results combined with the thermal information are used for identifying the nature of the mortars and for clarifying some technological aspects of the manufacturing technique. The results disclose the complex structure of the mortars and evidence weight changes due to dehydration, dehydroxylation and carbonates decomposition that allow to group the major part of the mortars in the well-distinct area of the hydraulic lime mortars with only a small group of mortars, used for bonding the stones of the cistern walls and also in few cases as first layer, to be grouped as lime mortars without hydraulic properties. (C) 2004 Elsevier B.V. All rights reserved.