Heidelberg , city (1994 pop. 139,430), Baden-Wurttemberg, SW Germany, picturesquely situated on the Neckar River. Manufactures include machinery, precision instruments, leather goods, and tobacco and wood products. Most important to Heidelberg, however, is the tourism industry. Primarily focused on the Heidelberg Castle, the trade brings in several million visitors per year. Heidelberg was first mentioned in the 12th cent. In 1225 it was acquired by the count palatine of the Rhine and until 1720 was the residence of the electors palatine. The Univ. of Heidelberg (Ruprecht-Karl-Universität) was founded in 1386 by Elector Rupert I and is the oldest German-speaking university after those in Prague and Vienna. It became a bulwark of the Reformation in the 16th cent., declined after the Thirty Years War (1618'48), and, recovering after the French Revolutionary Wars, became the leading university of 19th-century Germany. Student life in 19th-century Heidelberg, with its duels, songs, and romance, has been much publicized. The university's professors have included noted theologians, the chemist R. W. Bunsen, and the sociologist Max Weber. Since 1952 the city has been the headquarters of the U.S. army in Europe. Heidelberg is famous for its ruined castle (built mainly in the 16th and early 17th cent.), which was largely destroyed by French troops in the late 17th cent. In the castle's cellar is the Heidelberg Tun, a gigantic wine cask with a capacity of c.58,080 gal (2,200 hectoliters). Other points of interest in Heidelberg include the city hall (1701'03) and the Philosophenweg (Philosopher's Way), a path overlooking the city. The Heidelberg Catechism was a profession of faith of the German Reformed (Calvinistic) Church, drawn up at the request of Elector Frederick III and published in 1563. It gained wide repute and was adopted by several Reformed churches.