Kolmården

thumb|Map of old border forests between Swedes and Geats. Kolmården is red, Tylöskog is green, and Tiveden is blue Kolmården () is a long and wide densely forested rocky ridge that separates the Swedish provinces of Södermanland and Östergötland, two of the country's main agricultural areas, from each other, and in historic times, along with Tylöskog and Tiveden, formed the border between the land of the Swedes and the land of the Geats.

==History== In early medieval times it was seen as a major obstacle in land travel between the regions, and so the Baltic Sea was largely used instead. Together with the extensive forests of Tiveden and Tylöskog to its west, Kolmården formed a major impediment for travel between the Swedes in Svealand to the north and the Geats in Götaland, which caused peaceful and warlike interaction to be conducted by water.