Moscow is the capital of Russia. The city is located in western Russia and lies in the broad, shallow valley of the Moskva River, a tributary of the Oka and thus of the Volga, in the centre of the vast plain of European Russia. This region is one of the most highly developed and densely populated areas of Russia. The climate of Moscow is of the continental type, modified by the temperate influence of westerly winds from the Atlantic Ocean. Winters are cold and long, summers are short and mild . The moderate annual precipitation occurs predominantly in the summer months, often in brief, heavy downpours. Only a small percentage of Moscow's population is employed in the city centre because of the decentralization of workplaces. Industry is the dominant source of employment, followed by science and research. Although Moscow's role in the country's administration is of prime importance, government as a source of employment is relatively minor. Engineering (production of automobiles and trucks, ball bearings, machine tools, and precision instruments) and metalworking are by far the most important industries. Other important activities include the manufacture of textiles, chemicals and derivative products, and consumer goods (foodstuffs, footwear, and pianos); timber processing; construction; and printing and publishing. Moscow is the headquarters of state insurance and banking organizations. The pattern of rings and radials that marked the historical stages of Moscow's growth remains evident in its modern layout. Successive epochs of development are traced by the Boulevard Ring and the Garden Ring (both following the line of former fortifications), the Moscow Little Ring Railway, and the Moscow Ring Road. From 1960 to the mid-1980s the Ring Road was the administrative limit of the city, but several areas of the largely greenbelt zone beyond the road have been annexed since then. The centre of the city and the historical heart of Moscow is the fortified enclosure of the Kremlin. Its crenellated redbrick walls and 20 towers (19 with spires) were built at the end of the 15th century and were partially rebuilt in later years. Within the walls of the Kremlin are located the meeting places of the government of Russia. Among these are the former Senate building (1776-88), the Kremlin Great Palace (1838-49), and the modern Palace of Congresses (1960-61). Other features within the Kremlin include the central Cathedral Square, around which are grouped three cathedrals, all examples of Russian church architecture at its height in the late 15th and early 16th centuries; a group of palaces of various periods; the white bell tower of Ivan III the Great; the Armoury Museum; and the Arsenal (1702-36). Along the east wall of the Kremlin lies Red Square, the ceremonial centre of the capital. The Lenin Mausoleum stands beneath the Kremlin walls, and the Church of the Intercession, or Cathedral of St. Basil the Blessed, is at the southern end of the square. The State Department Store, GUM, faces the Kremlin, and the State Historical Museum (1875-83) closes off the northern end of the square. In the remainder of central Moscow, within the Garden Ring, are buildings representative of every period of Moscow's development from the 15th century to the present. Examples of the Moscow Baroque style, the Classical period, and the revivalist Old Russian style may be found. In the Soviet period streets were widened, and much of the old part of the inner city was demolished and replaced by large office and apartment buildings, government ministries, headquarters of national and international bodies and organizations, hotels and larger shops, and principal cultural centres. Beyond the Garden Ring is a middle zone dominated by 18th- and 19th-century developments; many factories, railway stations, and freight yards are located there. Since 1960 extensive urban renewal has occurred, producing neighbourhoods of high-rise apartment buildings. The outer zone has been the site of modern factory development and extensive housing construction in the 20th century. Beyond the newer suburbs are areas of open land and forest, together with satellite industrial towns and dormitory suburbs. Moscow's inhabitants are overwhelmingly of Russian nationality, but members of more than 100 other nationalities and ethnic groups also live there. Population density, though lowered by outward expansion of the city, has remained high because of the vast number of large apartment buildings. Moscow has a large concentration of educational institutions, and its centres of higher education draw students from throughout Russia. Moscow State University (1755) is the leading educational institution. The city's many specialized educational institutions include the Moscow Timiryazev Academy of Agriculture and the Moscow P.I. Tchaikovsky State Conservatory. Scientific research is conducted by the Academy of Sciences of Russia and many institutions linked to industry. The city's libraries include the V.I. Lenin State Library. Theatre, music, and art are important in the city's life. The State Academic Bolshoi ("Great") Theatre (1825), Maly ("Little") Theatre, and Moscow Art Theatre are especially renowned. Of the many museums and galleries, the State Pushkin Museum of Fine Arts and the State Tretyakov Gallery are notable. Few people in Moscow own automobiles, necessitating heavy reliance on public transportation provided by the Metropolitan (Metro) subway, buses, streetcars, and trolleybuses. The Metro system, which reflects the city's street patterns, is known for the elaborate architecture of its stations. Moscow is the centre of the country's rail network, on which freight transport is heavily dependent. Trunk rail lines radiate from the city in all directions to major Russian population and industrial centres, to Ukraine, Belarus, and eastern Europe, and to Central Asia. Suburban commuter traffic is facilitated by the Moscow Little Ring Railway (1908) and the Greater Moscow Ring Railway, which link radial lines. Passenger trains connect to destinations throughout Russia and Europe. Moscow is also a major river port and is served by the Moscow Canal. The Volga's various canals link Moscow to all the seas surrounding European Russia. Moscow is the centre of the country's airline network; the Sheremetyevo airport, in the north, handles international flights.