Fuerte de Isla Verde Fuerte de Isla Verde ( ) was a military installation formerly located in Algeciras , Spain . It occupied the Isla Verde ( ) , which gave its name to the city as a whole ( via the Arabic name Al - Jazira Al - Khadra ' , , corrupted into " Algeciras " ) . The elongated island , which stood a short distance offshore of the city ' s old town , was already the site of an artillery battery in 1720 . In 1734 the fort was constructed on the island to the plans of the military engineer Juan de Subreville . Further remodeling took place in 1745 under Lorenzo de Solís . The installation , which followed the roughly triangular shape of the island , was initially equipped with three batteries . These were : The island was ringed by a masonry wall to block access to invaders . Several buildings occupied the interior of the fort . Up to 70 men could be accommodated in the living quarters , located next to the Algeciras Battery , which were divided into separate spaces for the officers and rank - and - file . A grocery storeroom was also located there . The gunners were quartered in a barracks next to the San García Battery , alongside the artillery store where gun carriages and spare gear was stored . The building was protected by a large shoulder to protect it from enemy fire . In the centre of the island was the main magazine , constructed with thick walls to reduce the risk that a projectile hitting the building would detonate the shells and ammunition stored inside . Drinking water was drawn from a well constructed nearby . There was only one entrance to the fort , in the northwest quadrant of the island adjoining the beach . This was the most vulnerable point of the structure so it was reinforced by external obstacles located on the beach . It was also reconfigured several times during the fort ' s existence to strengthen it . In 1810 most of Spanish fortifications around the Bay of Gibraltar were demolished by the British in 1810 , during the Peninsular War , to stop them falling into French hands . However , the fort at Isla Verde was not affected and underwent remodelling and reinforcement on several occasions during the 19th century . By 1821 the number of batteries had been increased to five . A number of firing positions were added to facilitate the use of musket s from the fortress walls and the batteries were paved with flagstones to make it easier to move the gun carriages around . But , during the course of the century the fort gradually fell into ruin . Deficiencies in its construction and erosion caused by the sea caused the structure to deteriorate , and in 1863 the Faro de Isla Verde ( ) was built on top of the old San García Battery . Improvements in artillery technology meant that by the start of the 20th century the fort had lost its previous military importance . In 1919 its management passed into the hands of the newly created Board of Harbour Works , which had to bear the cost of relocating the munitions stored there to a new magazine – which it also had to pay for – at Punta de San García . A breakwater was constructed to the north of the island to provide shelter for the construction of the docks of the Port of Algeciras . Military use continued for a while ; the fort was reoccupied during the Second World War when two bunker s with machine - gun posts were constructed and manned by a detachment of 40 soldiers , for whom a barracks and kitchen were built . The fort was partly destroyed in the 1960s when an expansion of the port resulted in warehouses and factories being built on the site . The fort was given protected status as an historical heritage site in 1985 and was awarded special recognition in 1993 by the Government of Andalusia . In 2006 , the Port Authority of Algeciras sponsored work to excavate and restore the surviving parts of the fort . The remains of the structure were partly reconstructed in an attempt to restore it to a semblance of its original appearance .