The section of the old city walls by the sea near the Fortaleza in Lagos is one of the oldest portions of the old defenses. The original sections are thought to date from the Carthaginian or Roman periods, with the walls successively having been improved by the Moors and, later, Christian rulers.

One should note the towers guarding the gate of São Gonçalo and to the North of the city, the wall which was extended in 1520 to protect the burgeoning new sections of the the city which resulted from increased trade during the period of the Voyages of Discovery.