It is believed the earliest settlement of Scotland was undertaken by hunters and fishermen 6,000 years ago. They were followed by the Celtic Picts, who survived to the 18th-century in the clan structure of the Highlands. In 1707, England persuaded the Scottish Parliament to agree to the union of two countries under a single parliament. The Scots received trading privilges and retained their independent church and legal system. The Scots used these trading privileges to strengthen their economy with kelp, potato, sheep, shipping, steel, coal, cotton and jute industries. During the last 30 years Scotland's economy has boosted due to Scottish Oil imported from the North Sea. The two major cities in Scotland are Edinburgh, the royal capital since the 11th-century, known for its historic buildings and architecture and home to a half million residents. The other major city is Glasgow, the largest in population.