The end of the Great Northern War resulted in the Treaty of Nystad in 1721, ceding much of the Swedish Empire's claim to the Baltic Sea to the rising Tsardom of Russia. Peter the Great already began construction of his new capital St Petersburg in 1703 after successfully capturing Swedish provinces on the eastern coast.[7] This strategic location allowed Russian access to the Baltic Sea through the Neva River that flowed to the Gulf of Finland. The island of Kotlin and its fortress Kronstadt northeast of St Petersburg provided a gateway and commercial harbor access owing to the shallowness of water closer to the city.[8]