Kronshtadt or Cronstadt (both: krənshtät´), city, NW European Russia, on the small island of Kotlin in the Gulf of Finland, c.15 mi (20 km) from Saint Petersburg. It is one of the chief naval bases for the Russian Baltic fleet. The harbor is icebound for several months each year. Kronshtadt and Kotlin are now connected to the mainland by the roadways associated with a flood-control dam built to protect St. Petersburg.

Kronshtadt was founded (1703) by Peter I as a port and a fortress to protect the site of St. Petersburg, and it was the commercial harbor of St. Petersburg until the 1880s. The port lost its commercial value after the development of St. Petersburg. The visit (1891) of a French naval squadron to Kronshtadt was followed by a Franco-Russian military agreement heralding the formation of the Triple Entente of France, England, and Russia.

Mutinies of the naval garrison took place in 1825 and 1882 and played a part in the revolutions of 1905 and 1917 (see Russian Revolution). A revolt of the sailors in Mar., 1921, was instrumental in establishing Lenin's New Economic Policy. The general unrest among peasants and workers touched off this mutiny of the naval garrison that had been loyal to the Bolsheviks during the revolution. This was the climax of the anti-Bolshevik unrest in the country. In World War II, Kronshtadt played a major role in the defense of St. Petersburg (then Leningrad) against the Germans.

Cronstadt: see Kronshtadt, Russia.