Are there no limits to human cruelty? Is there any divine justice? Do the gods even matter if they do not occupy themselves with rewarding virtue and punishing wickedness? Seneca's plays might be dismissed as bombastic and extravagant answers to such questions--if so much of human history were not ''Senecan'' in its absurdity, melodrama, and terror. Here is an honest artist confronting the irrationality and cruelty of his world--the Rome of Caligula, Claudius, and Nero--and his art reflects the stress of the encounter. The surprise, perhaps, is that Seneca's world is so like our own.