Classical authors, both Greek and Roman, wrote accounts of the occasions when the Celtic barbarians burst in upon their lands. One episode that left the Romans with something of a paranoid dread of the Celts was the sack of Rome itself, in about 390 BC.
Classical writers, living themselves in a martial society, were filled with admiration for the superb physique and indomitable courage of the Celtic warriors: 'a whole band of foreigners', wrote Ammianus Marcellinus, 'will be unable to cope with one of the Gauls in a fight, if he calls in his wife, stronger than he by far and with flashing eyes; least of all when she swells her neck and gnashes her teeth.'
At the same time the differences between Classical and Celtic culture provoked not only curiosity but often horror and disgust. Poseidonius noted wryly that 'the lower classes drink wheaten beer prepared with honey...They use a common cup, drinking a little at a time, taking no more than a mouthful, but they do it rather frequently.'
Diodorus Siculus observed with distaste that 'When their enemies fall they cut off their heads ... and these first-fruits of battle they fasten by nails upon their houses, just as men do, in certain kinds of hunting, with the heads of wild beasts.'
