The development of Cascais began in earnest in the 12th century, when it was administratively subordinate to the town of Sintra, located to the north. In its humble beginnings, Cascais depended on the products of the sea and land, but by the 13th century its fish production was also supplying the nearby city of Lisbon. The toponym "Cascais" appears to derive from this period, a plural derivation of cascal (monte de cascas) which signified a "mountain of shells", referring to the abundant volume of marine mollusks harvested from the coastal waters. During the 14th century, the population spread outside the walls of its fortress castle.
