Карл X Густав
Sweden and Denmark fought several wars during the 16th and 17th centuries. As a great deal of Denmark consists of islands, it was usually safe from invasion, but in January 1658, most of the Danish waters froze. Charles X Gustav of Sweden led his army across the ice of the Belts to besiege Copenhagen. The war ended with the treaty of Roskilde, a treaty very favorable to the Swedish.