The mild climate, access to water, quality of its soils and geographically advantageous location at the mouth of the Tagus River attracted early settlement to this region. The rugged hilltops of the interior conditioned cultivation and allowed the settlement of several small agricultural castros within the region's limits, such as Castro of Leceia (which was classified in 1963 as a property of public interest). This archaeological site is a witness to the early settlements and defensive structures that developed during the Chalcolithic period, although Paleolithic camps such as "Gruta da Ponte da Laje" are indicative of earlier settlements.