On 22 November 1850, Napoleon III declared: "Six thousand condemned men in our prisons weigh heavily on our budget, becoming increasingly depraved and constantly menacing our society.
I think it is possible to make the sentence of forced labour more effective, more moralising, less expensive and more humane by using it to further the progress of French colonisation."
Only a small number of men ever stayed in Saint-Laurent for long, and they were nearly all employed in the penitentiary administration or were considered harmless and unlikely to try to escape.
When a ship (such as La Loire or La Martinière) arrived from Saint-Martin-de-Ré, the first order of the day was to separate the "chevaux de retour" (literally "returned horses", but meaning the escaped prisoners) and the recidivists from the rest, to send them to the Îles du Salut, from whose shores escape was considered impossible.
Since there was a hospital in Saint-Laurent, many prisoners faked illnesses to get sent there, where they had plenty of time to plot escapes (as experienced and written by, among others, Charrière).