At the beginning of the Age of Discoveries, Oeiras became the industrial and commercial warehouse of Lisbon. The development of the Gunpowder Factory () in Barcarena was therefore important in the expansion of the Portuguese dominions of the Orient, in addition to the aggregate extraction and calcium oxide furnaces in Paço de Arcos. These industries were supported and guarded by the construction of several fortifications along a maritime defensive line that ringed the southern coast to Lisbon and that controlled navigation in the Tagus estuary from the 16th to 18th centuries. This perimeter included the Fort of São Lourenço da Cabeça Seca (also known as the Lighthouse or Tower of Bugio), rising from a tiny islet in the middle of the Tagus River, as well as the Fort of São Julião da Barra, both examples of Renaissance military architecture.