In 1219 Waldemar II of Denmark established a fortress on the site. The town gained commercial importance by the turn of the century, and in 1346 was sold by Denmark to the Teutonic Knights. Sweden acquired Tallinn 215 years later, and it was annexed by Russia in 1710. The Russians used the city as a naval base for the Baltic fleet, but lost it for a while to the Germans during World War II. August 1991 - Estonia gains independence. March 29, 2004 Estonia is accepted into NATO. It's the first time in its history to join a military alliance voluntarily. May 1, 2004 Estonia joins the European Union.