Evaluation of the shelters over the prehistoric Megalithic Temples of Malta: environmental considerations

Two of the seven prehistoric Megalithic Temples of the Maltese Islands inscribed on the UNESCO World Heritage List were covered by a temporary open-sided shelter in 2009. This was to protect the Temples from environmental factors, primarily direct rainfall and insolation, which were considered as main causes of deterioration of both the materials and the structures. The sheltering was preceded by intense environmental monitoring which lasted for 1 year and which was then partially continued even after the sheltering. This paper, evaluates the changes in environmental conditions both before and after sheltering and concludes that the advantages of the shelter far outweigh the disadvantages. Caution is, however, advocated in the case of noted disadvantages, such as salt, dust and pollution accumulation on the now protected megaliths, which should continue to be carefully monitored for any possible deleterious effects. Recommendations are also given for maintenance actions which can prevent these events from negatively affecting the state of conservation of the megaliths. These include the dry, soft regular brushing of the megaliths, and the surrounding ground, to remove accumulated salts which can cause the limestone to deteriorate if reabsorbed back into the porous stone either during RH fluctuations or on occasions when condensation events, which have been detected during the monitoring campaign even after the sheltering, occur.