The power of Athens declined following its defeat in the Peloponnesian War against the Spartans. From that time on, the theatre started performing old tragedies again. Although its theatrical traditions seem to have lost their vitality, Greek theatre continued into the Hellenistic period (the period following Alexander the Great's conquests in the fourth century BC). The main Hellenistic theatrical form was not tragedy but 'New Comedy', comic episodes about the lives of ordinary citizens. The only playwright from the period whose work has survived is Menander. One of New Comedy's most important contributions was its influence on Roman comedy, an influence that can be seen in the surviving works of Plautus and Terence.