From 1803 to 1815 Britain was at war with Napoleonic France and many thousands of prisoners were taken. To help accommodate them redundant warships were commissioned as floating prisons known as ?the hulks?. Several hulks were at anchor at Plymouth among other places and conditions were so bad with poor sanitary arrangements, little exercise, lack of fresh air and a poor diet, the death rate rose to an unacceptable level and a prison on land was decided upon. Princetown on Dartmoor was considered a suitable location and that is how Dartmoor Prison came to be built.
Sir Thomas Tyrwhitt, founder of Princetown and a close friend of the Prince of Wales (who owned the land) was instrumental in deciding where the prison should be built and he it was who laid the Foundation Stone on 20th March 1806 when building work began. The first prisons were constructed from stones obtained by breaking up the boulders lying around the site supplemented by dressed stone from nearby Herne Hole quarry (owned by Mr. Tyrwhitt). Construction planned for completion in just a year and a half took twice as long due to labour disputes and the notorious Dartmoor weather.