The Kasbahs of Chellah and Oudayas (world cultural heritage) are the most important archaeological Roman and Islamic sites of the imperial city Rabat (Morocco). Submitted to natural hazards and environmental aggressions, these monuments have undergone marked degradation, visible on all sides.

An interdisciplinary analysis involving different geological disciplines and environmental factors was performed to introduce an innovative restoration method intended to reduce their progressive degradation.

Gravitational instability (e.g. Oudayas) and erosion (e.g. Chellah) from fluvial-littoral geomorphological processes, regional seismicity, and certain anthropic activities are the main degradation processes to be reduced by following the proposed recommendations.

Our studies have evidenced that the ancient Phoenician building techniques, still applied for reconstruction and preservation, result in the rapid and recurring deterioration of the old walls. Materials used to construct the Oudayas and Chellah walls consist of the calcarenite (or «Salé stone» from quarries near Rabat), mainly with bad geomechanical properties used in outdoor building. Hydrated lime mixtures, and the hydrated lime:water ratio, of mortars also have bad quality. The urban water quality to be used for restoration may require the application of special cements and mortars for restoration.

A most satisfactory restoration-test was performed (Chellah, July 2006), taking into account our new analytical data. This method may be applicable to restoring the old Almohade and Oudayas walls (more than 10.5 km in Rabat), in order to reduce the alteration and degradation processes which systematically strike the archaeological sites of Chellah and Oudayas.

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