The construction of Fort Santiago with hard stone, together with the original fortified walls of Intramuros, commenced in 1590 and finished in 1593 during the reign of Gómez Pérez Dasmariñas. The stones used were volcanic tuff quarried from Guadalupe. The fort as Dasmariñas left it consisted of a castellated structure without towers, trapezoidal in trace, its straight gray front projecting into the river mouth. Arches supported an open gun platform above, named the battery of Santa Barbara, the patron saint of all good artillerymen. These arches formed casemates which afforded a lower tier of fire through embrasures. Curtain walls of simplest character, without counter forts or interior buttresses, extended the flanks to a fourth front facing the city.