Reutlingen is a city in Baden-Württemberg, Germany. It is the capital of the eponymous district of Reutlingen. As of April 2008, it has a population of 109,828. Reutlingen has a university of applied sciences, which was founded in 1855, originally as a weavers' school. Today Reutlingen is home to an established textile industry and also houses machinery, leather goods and steel manufacturing facilities. It is famous for having the narrowest street in the world, Spreuerhofstraße (width 31 cm).
The first settlements in the area are believed to date from the 4th or 5th century. Some time around 1030, Count Egino started to build a castle on top of the Achalm, one of the largest mountains in Reutlingen district (about 706 m). One of the towers of this castle was rebuilt in the 19th century and is open to visitors. The name Reutlingen was first mentioned in writing in the so-called Bempflingen Treaty which is dated approximately 1089–90.
Around 1180, Reutlingen received market rights and, between 1220 and 1240 it was promoted to city status and city-walls and fortifications were built. Shortly thereafter, from 1247–1343, the town's landmark, the St. Mary's Church was built.
In 1377 Reutlingen was the scene of a victory by the Swabian League, formed in the previous year by 14 Swabian cities, led by Ulm, over the Count of Württemberg. In 1519, a later Swabian League came to Reutlingen's help when Ulrich, Duke of Württemberg attempted to seize the city; the League landed a crushing blow, conquering Württemberg and selling it to Charles V.
As a result of such struggles, Reutlingen became an Imperial City of the Holy Roman Empire, free from allegiance to the Duke of Württemberg. In 1530, Reutlingen's city council signed the Augsburg Confession, and in 1580 and the Formula of Concord, key documents of Lutheranism. In 1803, in the wake of the French Revolutionary Wars, Reutlingen lost its independence in the German Mediatisation, being restored to Württemberg.