Due to the expansion of Russia in the 18th century in the Baltic Sea, Sweden, until then the dominant power in this sea, had to develope its fortifications from Finland, in those times still part of the Swedish kingdom. As part of this plan, in 1748 it commenced the construction of the gigantic Sveaborg (Fortress of Svea) on six islands (Kustaanmiekka, Susisaari, Iso-Mustasaari, Pikku-Mustasaari, Länsi-Mustasaari and Långören) located near Helsinki, intended to defend the city, but also to be an important naval base.
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