Introduction As exemplified by the open air art and habitation sites of the Douro basin, particularly those recently found in the Côa valley (Zilhão et al . 1997), the interior of Iberia knew an important settlement throughout the Upper Palaeolithic. However, after the end of the Ice Age, c . 11,400 calendar years ago, it shows no sign of human occupation (with the exception of some areas in the upper Ebro basin) until 5000–4500 BC, when the protagonists of such occupation are already clearly defined agro-pastoral societies. This pattern seems to be a genuine reflection of regional settlement history. Many systematic survey projects in both Portugal and Spain (Iglesias et al . 1996, Arias 1997) have consistently identified large numbers of late early Neolithic (epi-Cardial or Impressed-Ware) sites all over this vast area, as well as, particularly in Portugal, fair numbers of Upper Palaeolithic sites. None, however, is of Mesolithic age, and there is not a single typical Cardial sherd. The abandonment of the Iberian interior in the early Holocene may be related to the particular geographic and climatic characteristics of the peninsula. Unlike European areas north of the Pyrenees where Mesolithic occupation of the hinterland is well documented, the Meseta lacks important lakes, and the rivers, even the largest (such as the Douro, the Tagus, and the Guadiana), are susceptible to drying out in the summer. Therefore, aquatic resources, which were critical in known Mesolithic instances of successful settlement of mainland Europe (as along the Danube), may have been subject to periodic failure in interior Iberia.
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