Gibbon, Edward.Decline and Fall of the Roman Empire. Knopf, 1994. Classic and still controversial account by the 18th-century historian; also available in abridged editions.
Nardo, Don.The Roman Empire. Lucent, 1994. Traces the history of the empire from the Republic to the fall of Rome. Appropriate for students.
Suetonius.Trans. Robert Graves.The Twelve Caesars. Penguin, 1979. The original source of biographical information on the rulers of Rome, written in the 2nd century.