Kronstadt, also spelled Kronshtadt, Cronstadt or Kronštádt is a Russian port city in Kronshtadtsky District of the federal city of Saint Petersburg, located on Kotlin Island, 30 kilometres west of Saint Petersburg, near the head of the Gulf of Finland. It is linked to the former Russian capital by a combination levee-causeway-seagate, the St Petersburg Dam, part of the city's flood defences, which also acts as road access to Kotlin island from the mainland.
Founded in the early 18th century by Peter the Great, it became an important international centre of commerce whose trade role was later eclipsed by its strategic significance as the primary maritime defence outpost of the former Russian capital. The main base of the Russian Baltic Fleet was located in Kronstadt, guarding the approaches to Saint Petersburg. In March 1921, the island city was the site of the Kronstadt rebellion.
The historic centre of the city and its fortifications are part of the World Heritage Site that is Saint Petersburg and Related Groups of Monuments.
Kronstadt has been a place of pilgrimage for Orthodox Christians for many years due to the memory of Saint John of Kronstadt.