Saima

Saimaa is a large lake system in southeastern Finland, divided by islands and narrow channels into many named basins. Its waters drain by the Vuoksi River toward Lake Ladoga. The waterways also formed part of a contested frontier between Sweden and the Russian lands. In 1475 Erik Axelsson Tott founded Olavinlinna, or St Olaf's Castle, on an island between the Haukivesi and Pihlajavesi basins. The surrounding lakes impeded a potential attack, while trade grew around the stronghold and the town of Savonlinna received its charter in 1639. After wars between Sweden and Russia, the Treaty of Åbo in 1743 ceded the castle and its region to Russia. The lake's channels and islands thus shaped both movement and defence in the surrounding country.