Gvardeysk (Гварде́йск), known prior to 1946 by its German name Tapiau () (Tepliava; Tapiawa/Tapiewo), is a town and the administrative center of Gvardeysky District in Kaliningrad Oblast, Russia, located on the right bank of the Pregolya River east of Kaliningrad. Population figures: It is located within the historic region of Sambia.
Peter of Dusburg wrote of a settlement known as Tapiow, first documented in 1254, and the neighboring fort Surgurbi built by 1265. The Old Prussian names were derived from the words tape, teplu, toplu, tapi, meaning "warm", and sur garbis, meaning "around the mountain". During the 13th century Prussian Crusade, the area was conquered by the Teutonic Knights. To protect Samland from the Nadruvians and Scalvians, the crusaders built a wooden fort between the Deime and Pregel Rivers in 1283–1290. This was replaced by Tapiau Castle, a stone Ordensburg, in 1351.
The settlement gradually became known by the German crusaders as Tapiau. Vytautas, the later Grand Duke of Lithuania, was baptized in Tapiau in 1385. Upon the request of the anti-Teutonic Prussian Confederation in 1454 Polish King Casimir IV Jagiellon incorporated the region and town to the Kingdom of Poland and the Thirteen Years' War broke out. After the defeat of the Teutonic Knights in the war, in 1466, the town became part of Poland as a fief held by the Teutonic Knights. After the transfer of the Grand Master's seat from Malbork to Königsberg, Tapiau became the site of the Order's archives and library from 1469 to 1722.
Tapiau became a part of the Duchy of Prussia, a vassal state of Poland, in 1525. The Tapiau Castle was often used as a second residence of the Prussian dukes; Albert of Prussia died there in 1568. It became a part of the Kingdom of Prussia in 1701, receiving town privileges from King Frederick William I of Prussia in 1722. It became a part of the newly established Prussian Province of East Prussia in 1773 and was administered in Landkreis Wehlau (1818–1945). Tapiau became a part of the German Empire during the unification of Germany in 1871.