The Tunnels

An extract from “The Tunnels of Gibraltar” by MS Rosenbaum and EPF Rose published by The Gibraltar Museum under the auspices of The Gibraltar Heritage Trust.

Gibraltar’s historical role as a fortress guarding the maritime passage east-west through the Strait connecting the Mediterranean Sea with the Atlantic Ocean and narrowly separating the European and African Continents is well known. Its limited land area and its role as a fortress have combined to make the demand for underground facilities a pressing local problem of applied geology, and stimulated almost uniquely imaginative solutions to maximise protection and survival of both civilian and military personnel. Thus tunnels through the Rock have been excavated intermittently from the late 18th Century almost to the present day, and now total an incredible 30 miles (50 kilometres) within the Rock itself whose main ridge area measures only one and a half by one mile. Geological features of the Rock have profoundly influenced their construction.

The oldest visible evidence of a man-made excavation is an underground chamber associated with the collection of groundwater at Nun’s Well, near Europa Point at the south-east tip of the peninsular, a historical site now under the protection of the Gibraltar Government. This early Moorish cistern, dating back probably from the 8th century or possibly even earlier from Roman times, collects water from a Rock fracture that drains through the Gibraltar Limestone of the higher Windmill Hill Flats plateau extending north towards the Main Ridge. Details of the site have been recorded by Palao (1979).

Such early excavations were small, isolated, and relatively insignificant, apart from a large reservoir excavated much later near the Moorish Castle, to provide the first “town” water supply. Five distinct periods of major and significant tunnelling works were to follow:


The early tunnelling period, from the Great Siege of 1779-83 when tunnelling first began until about 1800 when the Galleries overlooking the isthmus forming the North Front were completed.


After a long gap in which there had been no tunnelling, the Admiralty, the Army and the City Council all began to go underground to excavate magazines, communications tunnels and reservoirs.


Construction of reservoirs for water storage, and more particularly construction of air raid shelters and underground hospitals, caused much tunnelling activity.


The greatly increased war garrison required new accommodation space, and space for food, equipment and ammunition.


The existing tunnels were linked together in a more efficient manner and additional storage chambers and reservoirs were hewn out of the Rock.

In total some 30 miles of tunnels and chambers now honeycomb the Rock, but since little more than one thousandth part of the Rock has been removed, there need be little anxiety that it has been riddled to the point of collapse!

Early fortifications overlooking the North Front were trenches cut in the solid rock or built up with masonry: the King’s Lines constructed prior to British capture of the Rock in 1704, the Prince’s Lines excavated between then and the siege of 1727, and the Queen’s Lines during the Great Siege of 1779-83. It was during the Great Siege that an attempt to mount guns so as to bring flanking fire on the enemy led to tunnelling behind the North face of the Rock overlooking the Isthmus by Sergeant-Major Ince and the Company of the Royal Artificers (a parent unit of the Corps of Royal Engineers). The original tunnel, now part of the Upper Galleries network, was to have just been a passageway leading to a promontory known as the Notch. However, with the use of tunnelling techniques based on gunpowder, the miners found the atmosphere in the excavation almost unbearable due to fumes from blasting (they relied on gunpowder charges for loosening the rock, and the strength of their arms and skill with sledgehammer and crowbar for its excavation). A ventilation hole was therefore blasted sideways into the open air. The advantage of mounting a gun there was immediately apparent, so the plan was changed. The tunnel became a gallery, and in the end, 12 cannon embrasures were made within it. St George’s Hall and the neighbouring Cornwallis Hall (both completed 1784-5) added ten more embrasures, and a series of tunnels was developed to provide underground communication between the surface defensive walls and trenches (known as the Lines). At the northern end of the King’s Lines is a natural cave, which became the focal point of tunnelling activity, acquiring the name of Star Chamber. The system of galleries was effectively complete by 1800 and military tunnelling then ceased until the end of the 19th Century.

The second period began in 1880 when the railway tunnels in Camp Bay north to Rosia Bay bordering the southwest coast of the Rock were excavated to provide quarry access. Then in 1895 the army carried out underground works to extend some of the caves, known as Genista, beneath Windmill Hill converting them into Beefsteak magazine. The caves had earlier been explored and surveyed by J Fredrick Brome, governor of the military prison, with the assistance of the inmates; the name was given to commemorate his efforts, Genista being the Latin botanical name for the yellow-flowering shrub called Broom in English.

Soon after this, in 1898 to 1899, the Admiralty’s contractors drove the Dockyard tunnel east through the entire mass of Gibraltar to Sandy Bay in order to develop the quarries there. Additionally the continuing pressure on building space and the need for security led the Admiralty in 1901 to begin a four-year project to convert the natural Ragged Staff Cave bordering the western harbour area into a magazine. The approach tunnel had to be fully brick-lined when completed since it passed through the uncemented superficial (Alameda Sands) which covered the western flank of the Rock.

The construction of the modern water system commenced with the works of 1898 to 1900 to excavate four water reservoirs from the solid Limestone rock under the west side of Gibraltar. Each of these was 200 feet long, 50 feet high and had an average width of 20 feet, with a total capacity of 5 million gallons. The excavations were lined with bricks and thus rendered impervious. These reservoirs were fed with water collected from a rocky area on the upper slopes on the north-west corner of the Rock which was cleared of its natural vegetation and all the crevices filled with concrete.

As demand for water increased, further sources of supply were required and a scheme, an entirely original idea conceived by the then City Engineer of Gibraltar, was carried out consisting of forming a catchment area of 10 acres on the east side of the Rock and driving a tunnel half-a-mile long from east to west in order to form a channel with which to convey the water to the newly excavated reservoirs on the west side. The first catchment was constructed in 1903 on the sandy slope on the east side of the Rock where the average inclination was 3 to 2, i.e. about 34 degrees to the horizontal.

Between 1911 and 1915 another reservoir of 2,000,000 gallons capacity was constructed and the catchment area increased by a further 14 acres.

The 1930’s marked the third period of tunnelling as the political situation and the ever increasing strength of Nazi Germany prompted further underground activity; in particular the construction of air raid shelters and underground hospitals beginning about 1936. About the same time, the City Council was enlarging its water storage capacity by a further 5 million gallons. Between 1933 and 1938 they built Water Reservoirs Nos.6 to 9 leading off from Waterworks Tunnel, and made a start on No.10, the one on the far eastern end. (When war broke out the Garrison took over No.10, and erected within it a two storey brick-built storehouse and barracks, which were then, occupied by 4th Battalion The Black Watch for part of the War. The reservoir reverted to its intended use in 1945).

By 1939, the total length of tunnels in the Rock of Gibraltar was just 7 miles, having been increased from 5 miles length just prior to the First World War. The fourth period of tunnelling then saw a dramatic increase in tunnel length. After the evacuation of the British Expeditionary Force from Dunkirk and the collapse of France, with the entry of Italy into the War, and a powerful Germany dominating Europe, the strategic importance of Gibraltar was intensified. The Garrison had to be increased in size and strengthened, including preparations made to deal with possible siege conditions. The problem was urgent and vital; space became even more valuable; stores, food, and equipment had to be built up, and protected, and siege accommodation was required for the troops.

A tunnel system would meet these needs, and would give full protection from the then known types of air attack, as well as from sea and land bombardment.

In October 1940, the first Tunnelling Company (180) of Royal Engineers arrived and excavation commenced, as described in some detail by Haycraft (1946). Three more Companies were to join them. Although in the initial stage development started at the north end of the Rock, the most pressing need was for the provision of new accommodation for the rapidly growing garrison. The obvious starting place was the existing galleries, and the peace of Willis’s Gallery was broken after a lapse of almost exactly 150 years.

The embrasures in Willis’s, Queen’s and the Upper Union Galleries became barrack rooms fitted with double bunks, and from the top end of Willis’s a new tunnel was begun, which first linked to Water reservoir No.10, and then continued south as the Great North Road. Further south this became Fosse Way and it eventually reached the sea at the other end of the Rock. It was realised that the Main Base Area should be on the southeast side of the Rock, protected and hidden from Spain, but facing the Mediterranean.

By the end of the War there were something like 25 miles of tunnels cut in the Rock, and during this time about 35 million cubic feet of rock had been removed.

During the final, post-war, period of tunnelling the Army tunnellers were engaged on a variety of storage area developments such as Project ‘C’ for fuel storage as well as minor maintenance tasks. Two more water reservoirs, each of 1 million gallons capacity, and a further 10 acres of catchments and auxiliary channels were constructed between 1958 and 1961. Together with the Moorish Castle reservoir which provided the first “town supply”, these brought the total to 13 reservoirs with a combined capacity of 16,000,000 gallons. In 1960 construction of Keightley Way Tunnel commenced, but the last major project was to be the construction of Molesend Way between 1965 and 1967.

By April 1968, the Tunnelling Troop had been disbanded and all remaining tunnellers left Gibraltar on posting to other Units. The responsibility for the maintenance of the existing tunnels then fell upon the Gibraltarian Ministry of Works and the British Ministry of Public Building and Works (later to become the Gibraltar Public Works Department and the Property Services Agency of the Department of the Environment respectively).