Kostroma (kəstrəmäˈ) [key], city (1989 pop. 278,000), capital of Kostroma region, E European Russia, on the Volga at the mouth of the Kostroma River. It is a major linen-milling and textile machinery center. Founded in 1152, it was the capital of a principality in the 13th and 14th cent. It became an important commercial center after it was annexed by Moscow in 1364. At Kostroma in 1613, Michael Romanov was elected czar. Among the ancient buildings of Kostroma are the Ipatyev monastery (16th cent.) and the Uspensky Cathedral (c.1250).