The defenses date back to the Northern War between Russia and Sweden in the early 18th century.
Archaeologists from Saint Petersburg State University have discovered old Swedish bastion redoubts on the southern shore of the Gulf of Finland, a spokesman for the University told Saint-Petersburg TV Channel.
The defenses dating back to the Northern War between Russia and Sweden are located on Cape Kolgompya on the northeast part of the Soikinsky Peninsula in Leningrad Oblast.
The earth redoubts consisting of interior grounds, ramparts, mounds and a moat are thought to have been built in 17-18th centuries.
The expedition has also found lead bullets and fragments of a hand grenade used in that period.
In October 1708, the Russian and Swedish armies met in a battle near Cape Kolgompya. Experts intend to continue studying the site and try and reconstruct the battlefield.