Chernyakhovsk (Черняхо́вск, formerly until 1946 known as Insterburg, ; И́нстербург; Įsrutis; Wystruć) is a town in Kaliningrad Oblast, Russia, and the administrative center of Chernyakhovsky District. Located at the confluence of the Instruch and Angrapa rivers, which unite to become the Pregolya river below Chernyakhovsk, the town had a population in 2017 of 36,423.
Insterburg was founded in 1337 by the Teutonic Knights on the site of a former Old Prussian fortification when Dietrich von Altenburg, the Grand Master of the Teutonic Knights, built a castle called Insterburg following the Prussian Crusade. During the Teutonic Knights' Northern Crusades campaign against the Grand Duchy of Lithuania, the town was devastated in 1376. The castle had been rebuilt as the seat of a Procurator and a settlement also named Insterburg grew up to serve it. In 1454, Polish King Casimir IV Jagiellon incorporated the region to the Kingdom of Poland upon the request of the anti-Teutonic Prussian Confederation. During the subsequent Thirteen Years' War (1454–1466) between Poland and the Teutonic Knights, the settlement was devastated by Polish troops in 1457. After the war, since 1466, the settlement was a part of Poland as a fief held by the Teutonic Knights.
When the Prussian Duke Albert of Brandenburg-Ansbach in 1525 secularized the monastic State of the Teutonic Order per the Treaty of Kraków, Insterburg became part of the Duchy of Prussia, a vassal duchy of the Kingdom of Poland. The settlement was granted town privileges on 10 October 1583 by the Prussian regent Margrave George Frederick. Insterburg became part of the Kingdom of Prussia in 1701, and because the area had been depopulated by plague in the early 18th century, King Frederick William I of Prussia invited Protestant refugees who had been expelled from the Archbishopric of Salzburg to settle in Insterburg in 1732. During the Seven Years' War, the town was occupied by Russia. During the Napoleonic Wars, French troops passed through the town in 1806, 1807, 1811 and 1813.