After the Ice Age, around 8,000 BC, there were already many people living in what is today the Stockholm area, but as temperatures dropped, inhabitants moved south. Thousands of years later, as the ground thawed, the climate became tolerable and the lands became fertile, people began to migrate back to the North. At the intersection of the Baltic Sea and lake Mälaren is an archipelago site where the Old Town of Stockholm was first built from about 1000 CE by Vikings. They had a positive trade impact on the area because of the trade routes they created.