Imperium is partly a biography, partly a novel, and wholly an attempt to re-create an actual long-lost book about the Roman lawyer, politician, and orator Cicero originally penned by his slave/secretary, Tiro. The result is not short on interesting historical tidbits. We learn, for example, that the punishment for killing a parent under Roman law involved a dog, a cock, and a viper. Yet, perhaps hamstrung by the truthiness of his task, Robert Harris (Fatherland) fails to breathe much life into his characters. ''This is not a textbook about the law,'' the author has narrator Tiro write at one point, but there are times when Imperium reads like one.