In 1698 and 1699, Peter the Great of Russia, Augustus II the Strong of Saxony and Poland–Lithuania, as well as Christian V and his successor Frederick IV of Denmark-Norway agreed on a three-front assault on the Swedish Empire, where minor Charles XII had ascended the throne in 1697. Holstein-Gottorp, just south of Denmark, was tied to Sweden by the marriage of duke Frederick IV to Hedvig Sophia, daughter of Charles XI of Sweden, in 1698. Danish forces entered Holstein-Gottorp in March 1700 and besieged the fortress of Tönning, while August the Strong was advancing through Swedish Livonia.