sentences:  When Sir Ralph Abercromby communicated in 1796 that he was transferring 4,000 prisoners from the West Indies, the Board began the search for a site for a new prison.The site was chosen because it was on the Great North Road only from London and was deemed far enough from the coast that escaped prisoners could not flee back to France.The site had a good water supply and close to sufficient local sources of food to sustain many thousands of prisoners and the guards.