Sheltering archaeological sites in Malta: lessons learnt

The purpose of this paper is to review the performance of the protective shelters installed over three archaeological sites in Malta over the past decade, and to draw some key lessons learnt that may be useful to others when considering whether to adopt a similar solution. The conservation threats to the Megalithic Temples of Malta are introduced and defined-these range from material issues (loss of surface) to structural issues (cracking and dislodgement of stones leading to structural instability and collapses). Causes identified specifically included fluctuating environmental conditions: wetting and drying cycles and thermal fluctuations, combined with the salt-laden Mediterranean island environment. The recognition during the late twentieth century of these issues as key factors in the deterioration of these structures, and the strategy that was developed in response, are outlined. A key component of this strategy was the installation of protective shelters over three of the main megalithic sites. The process through which the design requirements for the shelters were defined is reviewed. The performance of the shelters is then examined, through a critical review of unpublished reports and published studies. An evidence-based summary of the beneficial effects of the shelters is provided, and the possibility of any harmful effects discussed. A number of lessons learnt through this process are then identified. One key lesson is that the microenvironment in a newly-sheltered site is at a transitional stage that does not necessarily reflect longer-term trends, which therefore require long-term monitoring to be understood. The choice and number of environmental parameters to be monitored need to be informed by a careful consideration of their sustainability, both in terms of equipment and human resources. Any monitoring programme, however well-designed, needs to be open to re-evaluation and revision where needed. As more experience and data are accumulated from different sheltering projects, it will become more feasible to establish performance indicators in advance of a sheltering intervention, on the basis of which to evaluate its performance. The experience of these projects is then used to inform a checklist of key considerations for anyone considering whether to shelter an archaeological site. The foremost consideration is that every site requires a site-specific strategy tailored to its needs. The decision whether a shelter is desirable, and what its performance requirements should be, may only be taken in the context of such a strategy. This paper should help define the parameters for such a decision to take place.