Sovetsk (səvyĕtsk´), formerly Tilsit (tĬl´zĬt), town (1989 pop. 41,900), NW European Russia, on the Neman River at the mouth of the Tilse. It is a rail junction, a river port, and an industrial and commercial center in an agricultural area. Lumbering and woodworking are the chief industries; others include the production of machines, cotton cloth, and Tilsit cheese. The town grew around a castle built in 1288 by the Teutonic Knights and was chartered in 1552. Napoleon I, having won the battle of Friedland, met Emperor Alexander I of Russia on June 25, 1807, on a raft in the Neman River off Tilsit. Their negotiations, joined later by King Frederick William III of Prussia, an ally of Russia, led to the treaties of Tilsit of July 7 and July 9, 1807. By the first treaty, France made peace with Russia, which recognized the grand duchy of Warsaw and which secretly promised to mediate between France and England; if England should reject mediation, Russia was to ally itself with France. At the same time, France gave Russia a free hand with regard to Finland, then a Swedish possession. The Russo-French alliance proved tenuous and collapsed altogether in 1812. In the second treaty, Napoleon drastically reduced Prussia, which lost all its territory west of the Elbe to France and most of its Polish provinces to the grand duchy of Warsaw. Danzig became a free city, the Prussian army was reduced to 42,000 men, several leading Prussian fortresses were to be garrisoned by French troops, and Prussia was to join in the Continental System against England. Prussia was thus reduced to virtual vassalage to France, from which it freed itself only in 1813. Tilsit was occupied by Soviet forces in World War II and was transferred, along with other sections of East Prussia, to the USSR at the Potsdam Conference of 1945.