King’s Bastion is believed to have started as a Moorish city gate but was later developed by the Spanish in 1575[ to become the Spanish: Plataforma de San Lorenzo. Construction began in 1773, when Lieutenant-general Sir Robert Boyd (1710–1794), then Governor of Gibraltar, laid the first stone. The bastion was designed by Lieutenant colonel Sir William Green, Chief Engineer of the Soldier Artificer Company which later became the Corps. of Royal Engineers. At the time it was built, the King’s Bastion was the most important of Gibraltar’s defences on the west. Its arrowhead shape extended from the curtain wall fortification, known as the Line Wall, along Gibraltar’s western coast into the Bay of Gibraltar. It was consistent with traditional notions of a bastion. It included casemates, which fulfilled the need for barracks, and housed 800 men.Less than a decade later, in 1782, King’s Bastion served ably as the command post in the defence against the attacks of the French and Spanish during the Great Siege of Gibraltar. It was from the bastion, that the “Grand Attack” of the Spanish floating batteries was orchestrated. The floating batteries had been adapted to withstand heavy shelling and were anchored only 500 metres (550 yd) or so off the Rock. Designed by French engineer Jean Claude le Michaud d’Arcon they were equipped with specially reinforced hulls, irrigation pumps to quench any fires and pitched roofs to protect against plunging fire from shot. These modifications were thought to have made the ships unsinkable. The garrison quickly realised that red hot shots known as “hot potatoes”, were extremely effective against the floating batteries and they were all eventually destroyed by fire. It was from King’s Bastion that the first “hot potatoes” were fired at the Spanish floating batteries with great effect.
Return for 1859 show that there were seventeen 32-pounders, six 8-inch smoothbore weapons, and two 10-inch howitzers mounted in the Bastion. In 1874, the embrasures at the front of the bastion were remodeled to mount five muzzle-loading rifles (RMLs). All five RMLs had been mounted by 1878, where they remained until 1902. By the late 19th century, the bastion no longer served as a principal military defence. The turn of the century was remarkable for the reclamation of land in front of King’s Bastion, as part of the new dockyard. The bastion was adapted, and the casemates, no longer needed as barracks, housed coal stores. In addition, the area’s first electricity-generating station was built there, with construction starting in 1896.
During WW2 3.7-ins Anti Aircraft guns were mounted on the gorge of the bastion.