The Inundation was a flooded and fortified area of ground on the sandy isthmus between Spain and Gibraltar, created by the British in the 18th century to restrict access to the territory as part of the fortifications of Gibraltar. It was originally a marshy area known as the Morass at the far south-western end of the isthmus, occupying the area adjacent to the north-western flank of the Rock of Gibraltar. The Morass was dug out and expanded to create an artificial lake which was further obstructed by iron and wooden obstacles in the water. Two small fortifications on either side controlled access to Gibraltar. The only road to and from the town ran along a narrow causeway between the Inundation and the sea which was enfiladed by batteries mounted on the lower slopes of the Rock. The Inundation existed for about 200 years before it was infilled and built over after the Second World War.
Creation of the Inundation
Prior to the creation of the Inundation, the principal access to Gibraltar was via a narrow strip of land between the Morass and the cliff face of the Rock. During the Thirteenth Siege of Gibraltar, the Spanish had managed to dig trenches along this strip of land to reach within only 600 feet (180 m) of the walls of Gibraltar. A redan or flèche was built in front of the town's Landport Gate during the siege to overlook the Morass and provide additional defence. Oliver Cromwell had suggested in the previous century that a canal could be dug across the isthmus to make Gibraltar an island. Although this idea was not taken up, British commanders decided to make the Morass a more substantial obstacle and in 1735, it was dug out and flooded to form a pear-shaped lake connected to the sea via a short channel. The water in the Inundation was originally held back by a 4 ft (1.2 m) high dike, which allowed the 5 ft (1.5 m) high tide to replenish it, though this arrangement was changed in the 19th century. The Inundation restricted landward access to Gibraltar to two narrow passages on either side of the water, one immediately below the sheer cliff face of the Rock and the other, which was used as the main road into Gibraltar (now Winston Churchill Avenue), forming a narrow causeway known as the Strand between the sea and the Landport Gate. According to a late 18th-century author, the Inundation measured about 200 yards (180 m) in length by about 60 yards (55 m) broad and was "nearly man-height" in depth. To further restrict access, the British built two defended positions on either side of the northern end of the Inundation, not only to guard against a surprise attack but to prevent desertion by disgruntled members of Gibraltar's garrison. The Advance Guard Room was built on the east side on the foundations of an earlier Spanish fortification which had controlled movement across the strip of land adjoining the Morass. After William Green became Gibraltar's Senior Engineer in 1761, he had the Advance Guard Room (renamed Forbes' Barrier) more heavily fortified and also had the Bayside Barrier constructed on the other side to control access to the causeway. Both were surrounded by palisades.
In the 1760s, a line of spiked chevaux de frise was constructed across the top and bottom ends of the Inundation. Ditches twelve feet wide and three feet deep were dug across the Inundation on both sides of the chevaux de frise so that if the lake ever dried out it would still serve as a barrier. Another barrier was constructed at the south end of the Inundation, and stakes were driven into the bed of the lake to serve as underwater obstacles. An unnamed correspondent for the London Chronicle wrote on 19 April 1762: "thro' the middle [of the Inundation] we have run chevaux de frize, lined with plates of iron, and studded with iron spikes, one row pointing towards Spain, and the other towards the garrison, to prevent desertion. They are five feet high, sunk in the mud, and the spikes above the water; by clasping your hands together, your fingers extended and the backs up, you will have an exact idea of them. Through this inundation an enemy must march to come near us, for the causeway is narrow, and when the tide is at lowest ebb, thirty men could not march a-breast upon the beach and causeway; upon which point we can bring above 300 cannon and mortars to bear, besides wall-pieces and small arms." Iron hoops and "many other articles to entangle and obstruct an enemy" were also scattered across the bottom of the Inundation. Above the Inundation, the Rock of Gibraltar rose in a series of scarped steps which had been fortified with defensive walls, gun batteries and rock-cut trenches. The causeway was enfiladed by the King's, Queen's and Prince's Lines, by Willis' Battery above the lines and by still further batteries higher on the Rock, so that any enemy attempting to cross would be met by a hail of fire from several directions. In addition, the guns of the Grand Battery facing the isthmus were constantly trained on the causeway, as B. Cornwell recorded: "the guns on this battery are for this reason always kept charged with round and grape shot, and levelled just man-height from the surface of the isthmus; an artillery guard is also kept at this battery, and a lighted match constantly ready to apply to the cannon in case of necessity." A British clergyman, William Robertson, commented in an 1845 account of a visit to Gibraltar that "while crossing the causeway, the most inexperienced eye is struck with the terrible appearance of the batteries which command it, bristling with cannon, above and around." The Spanish called the landward approach to Gibraltar el Boca de Fuego, the "Mouth of Fire."
Use of the Inundation in later years
The fortifications around the Inundation became the subject of a bitter dispute in 1789, a few years after the conclusion of the Great Siege of Gibraltar, when works were carried out to improve the North Front defences. Sir Robert Boyd, the then Governor of Gibraltar, ordered that a projecting rock at Forbes's Barrier was to be cut away. Colonel Robert Morse of the Royal Engineers, Gibraltar's senior engineer at the time, was vehemently opposed as he feared that it would weaken the northern defences. His protests to the War Office in London resulted in a party of engineers being dispatched to review the situation. The work was halted and their report unequivocally condemned the project as a bad idea:
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