Alston Moor had some of the largest deposits of lead and zinc ores in Britain. Lead was probably mined in Roman times. The Romans built a fort at Whitley Castle, and pieces of lead ore and slag have been found there, though no other traces of their work remain. There are various references to the mines of the area between the 12th & 16th centuries. Most emphasise the value of the silver, which makes up a small (<1%) proportion of the lead ore. This made the mines of interest to the Crown, who charged rents on the silver production. When Sir Edward Radcliffe, Earl of Derwentwater bought the estate in 1629 for £2,500, the mines were believed to be virtually exhausted.