The classical unities were a dramatic convention derived by Renaissance critics, notably Ludovico Castelvetro (1505—1571), from the Poetics of Aristotle. There were three unities. That of place prescribed that the action of a play should always remain in the same place; that of action that there should be a single plot, with no sub-plots; that of time that the play's performance should last as long as the action depicted in it. This last was later amended to the action taking place within 24 hours.
In Italy and France for many years during and after the Renaissance it was expected that the unities would be regarded. They had little influence in Britain and Germany, which had different dramatic traditions.