Gibraltar (Arab. Jebel al-Tarik, mount of Tarik), a fortified rock on the S. coast of Andalusia, Spain, belonging to Great Britain, and giving name to a town and bay on its W. side, and to the strait connecting the Atlantic and the Mediterranean. Europa point, its S. extremity, is in lat. 36° 6' N., Ion. 5° 21' W. The rock forms a promontory, 3 m. long from N. to S. and about 7 m. in circumference. A low sandy isthmus, 1 1/2 m. long and 3/4 m. broad, connects it with the mainland of Spain, having the bay of Gibraltar on the west and the Mediterranean on the east. Two parallel rows of sentry boxes across this flat mark the Spanish and English lines, the space between them being called the "neutral ground." The N., E., and S. sides of the rock are steep and precipitous, and almost inaccessible. On the west it slopes down to the water; here are the town and the principal fortifications. The highest point is about 1,400 ft. above the sea. The rock is composed of gray primary limestone and marble, and was uplifted probably at a recent geologic period, as a marine beach exists more than 450 ft. above the sea. It is perforated by a number of remarkable natural caverns, all of which are difficult of access.

The largest, called St. Michael's, has a hall hung with stalactites reaching from roof to floor. Its entrance is 1,000 ft. above the sea, and it is connected with other caverns beneath it of unknown depth. From the sea the surface appears barren; but acacia, fig, and orange trees, and a variety of odoriferous plants, grow in sheltered places. The animal productions are a few kinds of birds, wild rabbits, snakes, and monkeys. The latter, the only wild monkeys in Europe, are of a fawn color and without tails. The climate is temperate and generally healthy, but about once in 12 years an endemic fever, known as the Gibraltar fever, prevails. Immense sums of money and a vast amount of labor have been expended on the fortifications of this stronghold. The most remarkable of the works are the galleries tunnelled in tiers through the solid rock, along the N. front. They are 2 or 3 m. long, and are wide enough to admit a carriage. At every 12 yards they are pierced with ports for guns, so as to command the bay and neutral ground. On the summit of the rock are barracks and fortresses, and strong batteries frown all along the slope on the W. side. More than 1,000 guns are now in position. The garrison consisted in 1872 of 4,308 men.

The cost of maintaining the fortress in 1867-8 was £420,-465; estimate for 1872-'3, £219,417.-The town of Gibraltar lies on a shelving ledge on the W. side of the rock, near its N. extremity, 65 m. S. E. of Cadiz; pop. in 1871 (exclusive of the garrison), 16,454, English, Spaniards, Jews, and Moors. It consists chiefly of one spacious street, called the Main or Waterport street, about 1/2 m. long and well paved and lighted. The town appears to be more populous than it really is, from the number of strangers visiting it. Great care is taken to prevent the increase of new residents, and foreigners are allowed to remain only during specified periods, and on giving security for good behavior. The principal buildings are the residences of the governor and lieutenant governor, the admiralty, naval hospital, barracks, and storehouses. There are also Protestant and Roman Catholic churches, four Jewish synagogues, seven regimental and two public schools, a theatre, several hotels, a lunatic asylum, and an almshouse. The garrison library, founded in 1793, contains upward of 20,000 volumes. The water used in the town and by the garrison is collected entirely from the roofs in the rainy season and kept in tanks under the houses. Although a free port, Gibraltar has but little trade.

British manufactures for the Barbary states and for other countries bordering on the Mediterranean are distributed through it to some extent. The chief imports are cotton and woollen goods from England; tobacco, rice, and flour from the United States; sugar and rum from the West Indies; and wines, silks, spices, tea, and wax from the East. The chief export is wine. The revenues are usually about £30,000, and the expenditures nearly the same. The entire administration of affairs is in the hands of the military governor.-The bay of Gibraltar, sometimes called Algeciras bay, is formed by the promontory of Gibraltar on the east and the mainland terminating in Point St. Garcia on the west. It is 4 1/2 m. wide from E. to AY., and about 6 m. long from N. to S. Its depth of water, which is 260 ft. at the entrance, gradually diminishes toward the head of the bay, affording good anchorage. The tide rises 4 or 5 ft. Several small streams empty into it on the west and north. Opposite Gibraltar, on the AY. side, is the Spanish town of Algeciras. On the British side shipping is protected by two long moles.-The strait of Gibraltar, the channel connecting the Atlantic and the Mediterranean, lies between the southernmost part of Spain, from Cape Europa to Cape Trafalgar, and the African coast opposite, from Ceuta point on the east to Cape Spartel on the west.

Its length from E. to AY. is about 36 m. The narrowest point is S. of Tarifa, where the opposite coasts are but 9 m. apart. From Europa to Ceuta point is about 15 m., and from Trafalgar to Spartel about 25. The greatest depth of water is 960 fathoms. Through the strait a strong central current, from 3 to 6 m. an hour, sets constantly from the Atlantic into the Mediterranean; and two smaller currents, one along each coast, ebb and flow with the tide, running alternately into the Atlantic and the Mediterranean. The excess of water thus flowing into the latter sea is necessary to supply the loss by evaporation. The rock of Gibraltar, though well known to the ancients, was not occupied until a comparatively modern period. By the Phoenicians it was called Alube, which the Greeks corrupted into Calpe. Ceuta, the African point opposite, called by the English Ape's hill, was the ancient Abyla. These two hills constituted the pillars of Hercules, named, not from the Greek hero, but from the Tyrian deity, whose worship the Phoenicians introduced into all their settlements. The strait was long regarded as the western boundary of the world.

The value of Gibraltar as a strategic point was first discovered by the Saracens, who, under their leader Tarik (or Tarif) ben Zeyad, landed there in April, 711. In the following year Tarik built a fortification on the height, and it was called thenceforward after his name. In 725 was erected the castle which is still standing at the X. end of the rock. The fortifications were further strengthened in 11G1 under the direction of Alhaug Yaix, a celebrated Moorish engineer. In 1309 the place was captured by the Christians under Guzman the Good, and recaptured by the Moors in 1333. In 1349 siege was laid to it again by Alfonso XI. of Castile, but raised in the following year on account of the plague, which carried off the king. Gibraltar was finally captured by the Christians under the duke of Medina Sidonia in 1462. Under the Spanish crown it was so strengthened as to be considered impregnable; but it was taken Aug. 4, 1704, by a combined English and Dutch fleet under Sir George Rooke and the prince of Hesse-Darmstadt, and held till 1713, when it was confirmed to Great Britain by the treaty of Utrecht. Early in 1727 the Spaniards attacked it with a large force, but raised the siege on the signing of preliminaries of a peace with Great Britain in May of the same year.

But the most memorable siege of Gibraltar was that of 1779-83, sustained against the combined land and naval forces of France and Spain. By June 21, 1779, all communication between the rock and the mainland was cut off, and in July the fortress was completely blockaded. The cannonading began in September on the part of the besieged, but the Spaniards did not open their fire nntil January, 1780. The attack and defence which followed fixed the attention of Europe for the next three years. On the part of the besiegers all the resources of war were brought to bear both, by land and sea. The best engineers of France and Spain directed the approaches; a powerful fleet anchored in the bay, and for three weeks an incessant bombardment was kept up from 80 mortars and 200 pieces of battering cannon. The garrison, commanded by Sir Gilbert Eliott (afterward Lord Heath-field), and numbering 7,000 men, made a heroic resistattce. On Nov. 27, 1781, they destroyed the enemies' works in a sortie, but the allies at once reconstructed them, and soon brought 1,000 pieces of artillery to play against the fortress, while 47 ships of the line and innumerable smaller vessels menaced it by sea, and an army of 40,000 men conducted the operations on land.

The whole enterprise was directed by the duke de Crillon. Meanwhile Admiral Rodney, having defeated the fleet of Count de Grasse, succeeded in throwing relief into the fort. In September, 1782, the allies attempted to silence the British fire by means of 10 enormous floating batteries constructed by the chevalier d'Arcon in such a manner as to be deemed invulnerable. Each was manned by a picked crew and mounted from 6 to 21 guns. On the 13th they were put in motion, and one of the most dreadful cannonadings known in history was opened on both sides. It continued for several hours with little advantage to either party, but late in the afternoon the effect of the red-hot shot from the garrison became apparent, and soon after midnight nine of the batteries were on fire. Of their crews about 400 men were saved by the exertions of the British; the rest perished by the flames, explosions, or drowning. The besieged had 16 killed and 68 wounded. Several attempts to storm the rock by land proved equally disastrous. The British received fresh reenforcements, and in February, 1783, the siege was raised on the signing of preliminaries of peace. In 1868 a proposal to surrender Gibraltar to Spain was agitated in England, but did not meet with public favor.

As the key to the Mediterranean and one of the chain of fortresses connecting Great Britain with her East Indian possessions, it is of incalculable value for a coaling station, a depot for war material, and a port of refuge.