Kronshlot is the father of all Kronshtadt's forts - it was built in 1704 and was the first Russian sea fortification of Baltic Sea. Peter the Great was the author of it's project. There was the 3-levels wooden tower of 36 meters height with 14 cannons. Summer 1704 the first battle was there with Sweden fleet which tried to get to the freshly erected Peter and Paul Russian fortress in the entry of Neva river.
The casemate's battery of 1850-63 is seen on the picture.