Lithuanian Crusade: After a month-long siege, forces of the Teutonic Order captured and destroyed Kaunas Castle (reconstruction pictured), which was defended by troops of the Grand Duchy of Lithuania.

The Lithuanian Crusade was a series of campaigns by the Teutonic Order and the Livonian Order under the pretext of forcibly Christianizing the pagan Grand Duchy of Lithuania. The Livonian Order occupied Riga in 1202 and in the 1230s they settled in Chełmno Land, a fief of Poland. They first conquered other neighboring Baltic tribes—Curonians, Semigallians, Latgalians, Selonians, and Old Prussians—in the Livonian Crusade and Prussian Crusade.

The siege of Kaunas was laid by the Teutonic Order on the newly built Kaunas Castle in spring 1362. It was the first brick castle built by the Grand Duchy of Lithuania. After a month-long siege, the castle was captured and destroyed. Its commander Vaidotas, son of Kęstutis, and 36 others were taken captive. The defeat, followed by the destruction of Veliuona and Pieštvė the following year, severely weakened Lithuanian defenses along the Neman River and opened central Lithuania to Teutonic attacks.

The Teutonic Order is a Catholic religious institution founded as a military society c. 1190 in Acre, Kingdom of Jerusalem. The Order of Brothers of the German House of Saint Mary in Jerusalem was formed to aid Christians on their pilgrimages to the Holy Land and to establish hospitals. Its members have commonly been known as the Teutonic Knights, having historically served as a crusading military order for supporting Catholic rule in the Holy Land and the Northern Crusades during the Middle Ages, as well as supplying military protection for Catholics in Eastern Europe.

Kaunas Castle is a medieval castle in Kaunas, the second-largest city in Lithuania. Archeological evidence suggests that it was built during the mid-14th century in the Gothic style. Its site is strategic—a rise on the banks of the Nemunas River near its confluence with the Neris River. About one-third of the castle stood at the beginning of the 21st century.