Pyrenees (Celt. byrin, a steep mountain), a mountain range of Europe, separating France from Spain, and extending from Capes Creus and Cervera on the Mediterranean to the S. E. angle of the bay of Biscay. The divisions of the two countries along the boundaries are, beginning at the east: in France, the departments of Pyrénées-Orientales, Ariége, Haute-Garonne, Hautes-Pyrénées, and Basses-Pyrénées; in Spain, Catalonia, Aragon, Navarre, and Guipúzcoa. The Pyrenees form the eastern half of the great northern barrier of the Iberian mountain system, their prolongation, the Cantabrian mountains, stretching to Cape Finisterre, the N. W. point of the peninsula. On the N. E. the Cévennes form a connecting link with the Alps. The direction of the chain is from S. S. E. to N. N. W.; its length is about 250 m., and its greatest breadth, excluding some of the remoter slopes, about 70 m. Near the middle its axis is deflected by an elbow, so that the line of the western half, if prolonged, would run about 20 m. to the south of the eastern portion. The Pyrenees generally consist of two parallel main ridges, from which transverse spurs extend far on either side. The southern ridge is the more elevated.

The chain is higher in the eastern than in the western portion, and attains its greatest altitude and extension in the centre. Here the double range encloses the valley of Arran, in which the Garonne takes its rise. Other streams break through the northern ridge, but the southern presents a vast unbroken wall. This main ridge lies S. of the political boundary, so that the loftiest peaks and most elevated passes belong to Spain. The highest summits are not found along this crest, but occupy projections to the south. The mass of the Maladetta, on the frontiers of Aragon and Catalonia, presents the two peaks of Nethou or Anethon and Maladetta, the former the culminating point of the chain (11,160 ft.). Mont Perdu (10,994 ft.), called in Spanish las Tres Sorores, and the Cylindre de Marboré lie further to the west. To the north of these are the Pic Posets and Pic de Vignemale, the latter the highest summit of the Pyrenees in France (10,791 ft.). Among the other principal summits are the Tour de Marboré, Pic Long, Montcalm, Pic de Néouvielle, Pic du Midi de Bigorre, and Pic du Midi de Pau, most of them upward of 10,000 ft. high.

Mont Canigou (9,134 ft.), near the E. extremity of the range, on the meridian of Paris, forms a bold projection in France. The summit line, very uniform for long distances, has a mean elevation of about 8,000 ft., the passes being as elevated as those in the Alps. - A remarkable feature of the Pyrenees is the almost complete absence of longitudinal valleys, the great depressions running transverse to the chain. These frequently meet near the crest, and form passes called cols or ports. Many of the valleys terminate abruptly in huge basins (cirques or oules) enclosed by perpendicular walls of rock, and often one basin is continued by others on a higher level in the manner of an amphitheatre, the streams descending from one into the other in magnificent cascades. There are about 12 such falls in the basin of Gavarnie, the descent of one being 1,400 ft. In places the peaks rise almost perpendicularly for thousands of feet, and the grandeur of the scenery is unsurpassed even in the Alps. The snow line is about 8,500 ft. on the N. side, and on the S. side about 1,000 ft. higher. The snow does not appear in continuous fields, but is rather confined to the summits.

Glaciers, the existence of which was until recently unknown, extend on the N. slopes of the highest peaks, above an elevation of 7,000 ft. There are a number of small lakes on the side of France. The passes of the Pyrenees are very numerous, but only a few are practicable for carriages. The principal, beginning at the east, are: the col de Pertus, the great highway between Perpignan and Gerona; the col de la Perche; col de Puymorens; port de Salo; the pass of Viella; the port de Venasque; the port d'Oo; the Brèche de Roland (9,193 ft.), almost inaccessible to the experienced smugglers of these mountains; the port de Gavarnie; the port de Canfranc, between Oléron and Jaca; the pass of Roncesvalles, between St. Jean-Pied-de-Port and Pamplona, memorable for the defeat of Charlemagne (see Roncesvalles); and the pass of the Bidassoa, leading through Irun. The railroad from Bayonne to Vitoria passes the western extremity. The greater part of the range forms an unbroken watershed between the Mediterranean and the bay of Biscay, but the eastern portion belongs exclusively to the basin of the Mediterranean. The principal rivers flowing toward the north are the Adour, Garonne, Ariége, and Aude. The southern slope is tributary to the Ebro, which receives the Segre and other considerable streams, and to the Llobregat. The Bidassoa, which traverses the charming valley of Bastan, forms the westernmost portion of the boundary line.

The opposite sides of the Pyrenees present a great contrast. Toward Spain the range rises in a succession of abrupt terraces, whose rugged faces support a scanty and stunted vegetation. On the side of France the descent is much more gradual. Here the spurs enclose fruitful valleys enriched with tine pastures and orchards, and extensive forests stretch far up the slopes, affording good timber for ship building. - The primary geological formations are granite, forming the nucleus of the chain, micaceous schist, and primitive limestone, which are flanked by bands of clay slate, graywacke, and blue limestone. Oolitic and chalk formations occur, and trap, basalt, and porphyry appear in scattered masses. The mineral wealth of the Pyrenees is great, embracing iron, copper, zinc, and lead, but only the first of these metals is extensively worked. The Ariége rolls particles of gold. The mineral springs, mostly sulphurous, have long been noted, the best known being those of Eaux Bonnes, Eaux Chaudes, Bagnères-de-Bigorre, Bagnères-de-Luchon, Baréges, and St. Sauveur, all in France. The climate is comparatively mild. The forest trees include the oak, beech, fir, yew, and pine, and in the more elevated regions are found the rhododendron, daphne, and willow.

Among the wild animals are the bear, wolf, lynx, and the izard, a species of wild goat. The inhabitants of the mountains are a vigorous race. Toward the east the little republic of Andorra has long maintained an independent existence. The Basques inhabit the westernmost portion of the chain. - The Pyrenees have repeatedly been traversed by hostile armies, from the time of Hannibal, who is supposed to have passed by the col de Pertus, to the present century. In 1813 they were the scene of encounters between Wellington and Soult. The treaty between Louis XIV. and Philip IV., known as the peace of the Pyrenees, was concluded on an islet of the Bidassoa, Nov. 7, 1659.