Quote Originally Posted by Wardog View Post
To expand on that, my understanding is that (in the UK at least) using prison as a punishment for general criminality is actually a very modern (19th century) idea.

Before then, prison/jail was primarily used for
a) Holding political prisoners/hostages.
b) Holding debtors until they managed to pay off their debts.
c) Holding suspects awaiting trial, and convicts awaiting punishment.
The capacity to operate prisons at that level is comparatively recent - there's the constant resource expenditure involved (which is a lot easier with current levels of food production, energy production, etc.), and then the material and construction costs of creating prisons in the first place. The latter of these gets really important in sufficiently ancient settings, prior to the development of any real masonry.