mountain system and region lying between the Black Sea (west) and the Caspian Sea (east) and occupied by Russia, Georgia, Azerbaijan, and Armenia.

The name Caucasus is a Latinized form of Kaukasos, which the ancient Greek geographers and historians used; the Russian Kavkaz is of the same origin. The ultimate derivation is thought to be from Kaz-kaz, the Hittite name for a people living on the southern shore of the Black Sea. This ancient nomenclature reflects the historical importance of the region: in Greek mythology the range was the scene of the sufferings of Prometheus, and the Argonauts sought the Golden Fleece in the land of Colchis (the modern Kolkhida Lowland of Georgia), which nestles against the range on the Black Sea coast. The ranges also became a major land route to the north for cultural diffusion of the Middle Eastern Fertile Crescent civilizations. The peoples of the region have exhibited an extraordinary ethnic and cultural diversity since early times: the Colchians, for example, as described in the 5th century BC by the Greek historian Herodotus, were black-skinned Egyptians, though their true origin remains unclear. In subsequent centuries, successive waves of peoples migrating across Eurasia added to and were molded by the more established groups in the region. Not surprisingly, a greater variety of languages is spoken in Caucasia than in any other area of similar size in the world.

Caucasia includes not only the mountain ranges of the Caucasus proper but also the country immediately north and south of them. The land north of the Greater Caucasus is called Ciscaucasia (Predkavkazye, or “Hither Caucasia”); that south of it is Transcaucasia (Zakavkazye, or “Farther Caucasia”). The whole region, which has an area of 170,000 square miles (440,000 square km), is, nevertheless, predominantly mountainous. It extends southward from the lowlands of the Kuma and Manych river basins in the north to the northern frontiers of Turkey and Iran in the south and so comprises the southernmost portion of Russia (including Dagestan and several other administrative units constituted on an ethnic basis) and the Transcaucasian republics of Georgia, Armenia, and Azerbaijan.

The Greater Caucasus range extends for approximately 750 miles (1,200 km) southeastward across the Caucasian isthmus from the Taman Peninsula, which separates the Black Sea from the Sea of Azov (Azov, Sea of), to the Abşeron Peninsula, which juts into the Caspian Sea east of the oil-rich port of Baku, Azerbaijan. The vast plains and highlands of Ciscaucasia stretch from the northern foothills of the Greater Caucasus to the Kuma-Manych Depression, running from the Sea of Azov to the Caspian Sea. Western Ciscaucasia consists largely of plains, such as the extensive lowland north of the Kuban River that slopes gradually upward to the foothills of the mountains farther south. Central Ciscaucasia includes the Stavropol Upland, characterized mainly by tablelands of limestone or sandstone separated by deep valleys; the Mineralnye Vody-Pyatigorsk zone to the southeast, where Mount Beshtau rises to 4,593 feet (1,400 metres) from the surrounding plateau; and, still farther to the southeast, the Terek and the Sunzha ranges, separated by the Alkhanchurt Valley. Eastern Ciscaucasia is a lowland traversed by the lower Terek River and, to the north beyond the sands of the vast Nogay Steppe, by the Kuma River. Both rivers flow into the Caspian Sea.

South of the Greater Caucasus, on the Black Sea coast, lies the alluvial Kolkhida Lowland, site of ancient Colchis. South of the range on the Caspian side, the Shirak Steppe, between the Greater and Lesser Caucasus ranges, falls sharply into the Kura-Aras (Kura-Araks) Lowland. At the centre of this extensive depression the Kura River receives its major right-bank tributary, the Aras (Azerbaijani: Araz) River (Aras River). To the northeast the hills of southeastern Kobystan separate the Kura-Aras Lowland from the Abşeron Peninsula; and to the extreme southeast the narrow Länkäran Lowland extends south between the Caspian Sea and the Talish (Talysh) Mountains (Talish Mountains), which reach elevations exceeding 8,000 feet (2,400 metres).

West of the Kura-Aras Lowland rises the Lesser Caucasus range, which is extended southward by the Dzhavakhet Range and the Armenian Highland, the latter extending southwestward into Turkey. East of Lake Sevan (Sevan, Lake) in the eastern Lesser Caucasus, the highest peaks rise above 12,000 feet (3,600 metres), while Mount Aragats (Aragats, Mount) (Alagöz), the highest peak in the range, rises west of the lake to 13,418 feet (4,090 metres). From their western sources in the Armenian Highland, the Kura and Aras rivers both flow around the Lesser Caucasus—the Kura to the north of the range and the Aras to the south—to their confluence in the east.

The greater part of Caucasia originated in the vast structural downwarp in the Earth's crust known as the Alpine geosyncline, dating from the Late Oligocene Epoch (about 28.5 to 23.8 million years ago), and the region thus reflects some of the same structural characteristics as the younger mountains of Europe. Northern and central Ciscaucasia have a platformlike construction, with a foundation of folded structures dating from the Hercynian orogeny (Hercynian orogenic belt) early in the Carboniferous Period (i.e., about 345 million years ago). Southwestern and southeastern Ciscaucasia lie on the margins of a vast downfold in the Earth's surface that arose later in the Alpine orogeny, producing, concurrently, broad subsidence on the lower courses of the Kuban and Terek rivers. The surface of most of Ciscaucasia is composed of Tertiary and Quaternary rock that is less than 65 million years old; on the Stavropol Upland, which was uplifted in the Late Miocene Epoch (11.2 to 5.3 million years ago), there are strata of folded, platformlike structures.

Structurally the Greater Caucasus represents a great anticline (upfold) uplifted at the margin of the Alpine geosyncline about 25 million years ago and subsequently altered by fresh cycles of erosion and uplift. Hard, crystalline, metamorphosed rocks such as schists and gneisses, as well as granites that predate the Jurassic Period (i.e., older than 206 million years), have been exposed at the core of the western sector, while softer, clayey schists and sandstones of Early and Middle Jurassic origin (206 to 159 million years ago) have emerged in the east. The spurs of the Greater Caucasus are composed of younger limestones, sandstones, and marls.

The Kolkhida and Kura-Aras lowlands are both structural depressions linked to the Alpine geosyncline; the former is related to the formation of the Black Sea, the latter to that of the Caspian. In the Kolkhida Lowland, the overall surface of deposits laid down less than 25 million years ago is broken, at the foot of the mountains, by the protrusion of slightly older sedimentary rocks. Younger rock also underlies the Kura-Aras Lowland.

The structures of the Lesser Caucasus, the Talish Mountains, the Dzhavakhet Range, and the Armenian Highland likewise originated from folds uplifted from the Alpine geosyncline. Whereas the western sector of the Lesser Caucasus and the Talish in the far southeast are formed chiefly of deposits laid down about 50 million years ago during the downwarp episode of the geosyncline, the central and eastern sectors of the Lesser Caucasus consist of sedimentary strata with areas of intrusive volcanic rock that is at least twice as old. Geologically recent volcanism and contact metamorphism (the intrusion of molten material into preexisting strata) everywhere have played a great role in shaping the landscape. The folded base of the Dzhavakhet Range and of the Armenian Highland, for example, is masked by volcanic debris from eruptions that occurred in the Tertiary and Quaternary periods, but to the east much older rocks emerge between the middle course of the Aras (Aras River) and the latitude of Lake Sevan.

The Kura (Kura River) (and Aras), Sulak, Terek, and Kuma rivers flow into the Caspian Sea; the Rioni and the Inguri flow into the Black Sea; and the Kuban into the Sea of Azov. In the spring, when snow and ice begin to melt, the rivers of the Greater Caucasus and some of those of the Lesser Caucasus begin a flood cycle that may last for six months. Other Transcaucasian rivers are characterized by shorter-term spring flooding, while the rivers of the southern slopes of the Greater Caucasus generally have summer floods as well. The rivers of Ciscaucasia, except those flowing from the Greater Caucasus themselves, characteristically freeze over in winter, flood in spring, and become extremely shallow and sometimes even dry up in summer. In the eastern and central Caucasus, brief storm flooding occurs frequently. The karst regions along some spurs of the Greater Caucasus contain rivers that intermittently plunge beneath the earth into caverns within the soluble limestone bedrock.

Lake Sevan (Sevan, Lake) in the eastern Lesser Caucasus is the largest lake of Caucasia; its overflow drains into the Hrazdan River, a tributary of the Aras. The higher elevations of the Greater Caucasus contain numerous small mountain lakes, while a number of saltwater lakes occur in the arid regions of northeastern Caucasia.

The Greater Caucasus has more than 2,000 glaciers (glacier), occupying about 1 percent of its total area. Some 70 percent of them occur on the cooler northern face, with a concentration on the higher central slopes. The largest—notably Dykhsu, Bezingi, and Karaugom glaciers, on the northern face, and Lekzyr and Tsanner glaciers, in western Georgia—are about 8 miles (13 km) long. The desolate flanks of Mount Elbrus are streaked by many glaciers.

The crest of the Greater Caucasus forms a barrier between the temperate mid-latitude and the subtropical climatic zones by impeding the movement of cold air masses from the north into Transcaucasia and, conversely, that of warm air masses into Ciscaucasia from the south. Thus, average January temperatures, which range from between 23 and 28 °F (−5 and −2 °C) in Ciscaucasia, are between 40 and 43 °F (4 and 6 °C) in the Kolkhida Lowland and between 34 and 38 °F (1 and 3 °C) in eastern Transcaucasia. In summer the temperature differences between north and south are slight, and there is a more noticeable contrast between the west, with its cooler maritime climate and average temperatures of 73 to 79 °F (23 to 26 °C) and the more continental east, with average temperatures from 77 to 84 °F (25 to 29 °C).

Ciscaucasia has a semiarid climate in the west and a drier, more desertlike climate in the east. In Transcaucasia, the Kolkhida Lowland has a humid subtropical climate with mild winters and an annual rainfall of 47 to 71 inches (1,200 to 1,800 mm). In the southeast the climate of the Länkäran Lowland is also humid subtropical but with a dry season at the start of the summer; and the Kura-Aras Lowland has a dry subtropical climate with mild winters and hot summers and an annual rainfall of 8 to 16 inches (200 to 400 mm) that is lower in the east. The Middle Aras Trough in the Armenian Highland has a climate like that of the lowland downstream but is not so warm.

In the Greater Caucasus, temperatures decrease and the growing season becomes correspondingly shorter with an increase in elevation; and more total precipitation falls on the mountain slopes than on the neighbouring plains. Above an elevation of approximately 6,500 feet (2,000 metres), a westerly air current prevails, strengthening maritime influences and greatly moderating climatic conditions; average air temperatures reach 18 °F (−8 °C) in January and 55 °F (13 °C) in August. Because the Greater Caucasus stands at an angle to the westerly air currents, the heaviest precipitation, reaching a maximum of more than 160 inches (4,000 mm), accumulates on the south- and southwest-facing slopes. In the higher elevations, a cold, alpine climate with high humidity prevails, and perennial snow cover shrouds the highest crests. Along the northern Black Sea coast, the climate is typically Mediterranean, with mild, rainy winters and dry summers.

The northern slopes of the Lesser Caucasus facing the southern slopes of the Greater Caucasus have a climate similar to that of the latter at corresponding elevations, with rainfall concentrated in the west. On the slopes of the Talish Mountains in the southeast, the climate is humid, with annual precipitation reaching 68 inches (1,725 mm). The Armenian Highland, despite its proximity to the Black Sea, has a much more continental climate than that of the Greater Caucasus at corresponding elevations; at 6,500 feet (2,000 metres), for example, the average monthly temperature in the Armenian Highland is 10 °F (−12 °C) in January and 64 °F (18 °C) in July. Snow cover throughout the southern highlands lasts for four to five months, while annual precipitation averages about 20 inches (500 mm), with a spring maximum. Overall, the climate of the upland plateaus is moderately cold and continental, giving rise to semiarid steppe grasslands, whereas the climate of the heights is more humid and alpine, with cool summers and cold, prolonged winters.

In western and central Ciscaucasia, steppe vegetation once prevailed on the region's rich black soils, but these areas now have been converted largely to agricultural land. Forest-steppe vegetation, with oaks and beeches dominating the overstory (forest canopy), is found on the higher ground of the Stavropol Upland, around Mount Beshtau, in the western part of the Sunzha Range, and in the northern foothills of the Greater Caucasus. Eastern Ciscaucasia is semidesert, with grasses and sagebrush (Artemisia) on the richer chestnut soils and saltworts where the soil is saline. Artemisia, saltworts, and ephemeral species characterize the arid Kura-Aras Lowland, and similar vegetation occurs in the Middle Aras Trough. In the Kolkhida and Länkäran lowlands, the original subtropical broad-leaved forests have given way to cultivation.

At the lower elevations of the mountains themselves, between 2,000 and 3,000 feet (600 and 900 metres), arboreal brushwood and broad-leaved forest predominates. On the Black Sea slopes of the Greater Caucasus and in the mountainous hinterland of the Kolkhida Lowlands, there are mixed forests of beech, oak, hornbeam, chestnut, and alder, with lianas and an evergreen undergrowth on terra rossa and yellow soils. In the Talish Mountains, forests of chestnut-leaf oak and Parrotia persica flourish on yellow soils, while farther north on the heights backing the dry Kura-Aras Lowland grow forests and brushwood of xerophytic (drought-resistant) species. On the northern face of the Greater Caucasus, oak forests predominate with a brushwood understory (community of low-growing plants).

At higher elevations of up to 6,500 feet (2,000 metres), both the Greater and the Lesser Caucasus support forests of oak, hornbeam, and beech on brown soils; these are superseded at yet higher elevations by forests of Caucasian elm and Nordmann fir in the west and southwest and, occasionally, by pine forests farther east. Feather grass and needlegrass cover the black soil of the steppes on the lava plateaus and plains of the Armenian Highland. Steppes and tall-grass meadows are also widespread among the mountains of Dagestan.

Above elevations of 6,500 feet (2,000 metres) in the Greater Caucasus and in the Transcaucasian ranges, mountain meadow vegetation covers three successive belts: subalpine, alpine, and subnivean. Finally, at about 10,000 feet (3,000 metres) begins the zone of glaciers and perpetual snow.

The fauna of the Greater and Lesser Caucasus includes certain endemic species—the West Caucasian and the Dagestanian mountain goat, or tur, the Caucasian black grouse, and the Caucasian mountain turkey, or ular—and even some endemic genera, such as the long-clawed mole vole (Prometheomys schaposchnikowi). Other common mammals include the chamois, red deer, bear, lynx, and fox. Ciscaucasia's fauna is related both to that of eastern Europe and to that of Central Asia; the latter connection is evident in the Kura-Aras Lowland, which is home to the Persian gazelle (Gazella subgutturosa), the long-eared hedgehog, the jerboa, and the jungle cat (Felis chaus). The fauna of the Talish Mountains, which includes leopard and porcupine, is related to that of more southerly territories, while that of the Armenian Highland is related to that of Anatolia, with its ground squirrel, or suslik (Citellus), and mountain jerboa (Allactaga williamsi).

The rural population of the Caucasus is unevenly distributed, with the most densely populated part of the region along the Black Sea coast. The Rioni River valley and several smaller valleys in Transcaucasia are intensively cultivated and support large farm populations, and the foothills of the mountains also have a considerable population density. The alpine regions of the Caucasus and the arid steppes and lowlands of the Caspian coast, however, are sparsely populated. Urban dwellers account for nearly three-fifths of the entire population, and in Armenia and North Ossetia the proportion is even greater. Three cities— Baku, Tbilisi, and Yerevan—have populations of more than one million.

Caucasia long has played a major role as a link between Europe and Asia, and through it the culture of ancient Mesopotamia spread northward. Indigenous cultures also arose; in particular, Caucasia was one of the most ancient centres of bronze working from the first half of the 2nd millennium BC. Autochthonous peoples of the Caucasus are mentioned by Herodotus and by later writers such as Strabo. In the centuries between preclassical antiquity and the 14th century AD, Caucasia underwent successive invasions by various peoples, including Scythians, Alani, Huns, Khazars, Arabs, Seljuq Turks, and Mongols. The region also remained in contact with the Mediterranean world. This history of invasions and distant contacts has left its imprint on the culture of the Caucasian peoples; Middle Eastern influences, in particular, disseminated Iranian languages on the one hand and Christian and Islamic religion on the other. The later history, beginning with a long period of rivalry between Ottoman Turkey and Iran, is marked by the advance of Russian culture, which penetrated farther and farther into Caucasia from the 16th century onward. Throughout this process, individual ethnic groups, under pressure from stronger neighbours, took refuge in the ravines of the mountain ranges to preserve themselves in isolation.

More than 50 different peoples inhabit Caucasia. Russians and Ukrainians, who constitute more than four-fifths of the total population of Ciscaucasia, speak Slavic languages of the Indo-European (Indo-European languages) family. The language of the Armenians (Armenian language) is also Indo-European but distinct from other groups of languages in the family. The Ossetes, the Kurds, the Tats, and the Talysh speak Indo-European languages of the Iranian branch (Iranian languages). The majority of the peoples, however, speak tongues that are sometimes classified as a Caucasian language “family,” (Caucasian languages) although there is no proof of any linguistic relationship between the Kartvelian (or South Caucasian) and North Caucasian languages. The most important Caucasian language is Georgian (Georgian language), spoken by a nation into which numerous groups have long been amalgamated. Georgian and its many dialects belong to the Kartvelian (Kartvelian languages) family, the other groups being the Abkhazo-Adyghian (Abkhazo-Adyghian languages) and the Nakho-Dagestanian (Nakho-Dagestanian languages) divisions of the North Caucasian family. The Abkhazo-Adyghian group comprises the languages of Kabardian (Kabardian language) (Circassian), Adyghian, and Ubykh, as well as Abaza (Abaza language) and Abkhaz (both of which have been strongly influenced by the neighbouring Georgian). The Nakho-Dagestanian group (Nakh languages) consists of the Nakh (Nakh languages) languages, including Chechen and Ingush, and the Dagestanian languages, chiefly represented by the Avar-Andi-Dido (Avar-Andi-Dido languages), Lak-Dargin (Lak-Dargin languages) (Lakk-Dargwa), and Lezgian languages. The Dagestanian group of Caucasian languages is quite distinct from the Turkic languages spoken in Dagestan—namely, those of the Kumyk and of the Nogay. Other Turkic languages of Caucasia include Karachay and Balkar, and the widely spoken Azerbaijani.

The geologically recent rock layers around the Greater Caucasus, notably in the Kura-Aras Lowland and beneath the Caspian Sea, contain oil-bearing deposits. These also occur, with natural gas, in the older rocks of Ciscaucasia, while in Dagestan there are oil, natural gas, and coal deposits. Metallic ores are associated with magmatic rocks thrust up from deep in the crust: magnetite iron occurs near Daşkäsän, in Azerbaijan; copper and molybdenum are found in several parts of the Transcaucasian upland; several metallic ores lie in the Greater Caucasus; and manganese is found near Chiatura, in Georgia. Building materials include the cement marls of Novorossiysk in Ciscaucasia south of the Taman Peninsula and the rose-coloured tuffs (tufas) of Mount Aragats in Armenia. The mineral-water springs of the Caucasus are known throughout eastern Europe.

This abundance of resources allowed the Caucasus to become one of the more economically developed regions of the Soviet Union. Nonferrous metals, hydrocarbons, and coal are extracted in large quantities. hydroelectric power has been well developed and is intensively used. Hydroelectric stations have been built on the Kura, Khrami (a right-bank tributary of the Kura), and Rioni rivers; on several rivers of the Greater Caucasus; and on the Hrazdan River of Armenia, where the river's considerable potential has been exploited by a chain of downstream stations. A number of large industrial centres in the Caucasus region produce cast iron and steel, locomotives, trucks and automobiles, rubber and other chemical products, cement, hard-metal alloys, textiles and footwear, and food and tobacco products.

The Caucasus region has some of the best conditions for agriculture in Eurasia. Mixed agriculture is practiced on the rich black soils of western and central Ciscaucasia. Tea, citrus fruits, the tung tree, and bamboo are grown in the humid subtropical lowlands and foothills regions of Transcaucasia. Other areas produce tobacco, grapes, and various fruits. Water from the numerous rivers of the Caucasus is used to irrigate the arid areas of eastern Ciscaucasia, the Kura-Aras Lowland, and the lands around the Middle Aras Trough. In the higher elevations of the Caucasus, the primary activity is livestock raising (mainly sheep and cattle), although the people there also grow some mountain crops and pursue a few domestic crafts.

With its beautiful beaches along the coasts of the Black and Caspian seas, the Caucasus also has become a popular resort area. Its mineral springs and year-round mild climate make it a conducive environment for the treatment of many illnesses. Millions of people from Russia and other countries come to the Caucasus each year to rest, receive medical treatment, and enjoy such recreational activities as mountaineering and skiing.

Railways are well developed in the Caucasus. Trunk lines ring each of the main mountain ranges and traverse the Caucasian isthmus through Transcaucasia; branches from the main lines run through many of the valleys. A dense network of highways is heavily used for the transport of passengers and cargo. Oil and natural-gas pipelines also crisscross the region. In addition, the lower reaches of the Kura, Kuban, and Rioni rivers are navigable.

Modern cartographic (cartography) studies of the region were begun by Russian scientists in Ciscaucasia about 1815, and some medium-scale maps were produced in 1862. Large-scale maps began to appear in 1866; and a survey of summit elevations in the Greater Caucasus, from 1881, provided the basis for the study of the range's glaciation. The first ascent of Mount Elbrus was achieved in 1829 by a Kabardin mountaineer, Killar Khashirov, who reached the eastern peak; the higher western peak was first climbed in 1874 by four Englishmen.

During the 20th century, much of the study of the Caucasus was carried out by Soviet researchers. Various components of the region's natural environment have been investigated, and integrated studies of the entire mountain system and of specific regions, such as those of Armenia, Azerbaijan, and Georgia, have been conducted. Highly detailed atlases also have been published.