Historically mining of tin (and later also of copper) was important in the Cornish economy. The first reference to this appears to be by Pytheas: "see above". Julius Caesar was the last classical writer to mention the tin trade, which appears to have declined during the Roman occupation. The tin trade revived in the Middle Ages and its importance to the Kings of England resulted in certain privileges being granted to the tinners; the Cornish rebellion of 1497 is attributed to grievances of the tin miners. In the mid-19th century, however, the tin trade again fell into decline. Other primary sector industries that have declined since the 1960s include china clay production, fishing and farming.