The first construction of a fort on the site was between 1410 and 1415. Improvements to this were deemed necessary as the Cascais Bay was constantly threatened by the English. In 1488 a medieval-style tower at the tip of the Point of Salmodo, to the southwest of the Bay, was begun under the orders of King John II of Portugal. The fort, known as the Torre de Santo António de Cascais, was designed to share, with artillery ships and two other fortresses, resistance to possible military attack on Lisbon. The other forts were the Belém Tower and the Fort of São Sebastião de Caparica, which are approximately opposite each other on the River Tagus closer to Lisbon. Construction of the fort of Nossa Senhora da Luz de Cascais was ordered by Philip I to provide further reinforcements. It began in 1594, designed by an Italian, Captain Fratino, following an unusual triangular design that took advantage of the existing Torre de Santo António de Cascais, which is incorporated as one of three bastions built into the Citadel. The fortress had an interior courtyard that allowed communication between the three bastions and access to the batteries, barracks and cisterns. Reinforcement and enlargement of the Citadel was subsequently carried out around 1648, under the control of King John IV. The structure underwent further modifications and repairs until 1755, when it suffered considerable damage as a result of the Lisbon earthquake.