To sleep very soundly. The earliest simile of this kind, now obsolete, is to sleep like a swine (pig/hog), which dates from Chaucer’s time. “I shall sleep like a top,” wrote Sir William Davenant in Rivals (1668), no doubt referring to a spinning top that, when spinning fast, is so steady and quiet that it seems not to move at all. This simile persists, particularly in Britain. To sleep like a log is more often heard in America, although it has English forebears back as far as the sixteenth century. An older cliché is to sleep the sleep of the just, meaning to sleep soundly, presumably because one has a clear conscience. Its original source is a 1695 translation of a passage from the French dramatist Jean-Baptiste Racine’s Summary of the History of Port-Royal.