The Greeks gave the name Keltoi to the barbarian peoples of central Europe, who came down in their raiding parties from the fifth century BCE and terrorised the settled city-states of the Mediterranean. During the late fifth century these tribes expanded westwards into Gaul, Britain and Ireland, southwest into Iberia, southwards into northern Italy and eastwards through the Balkans and into Asia Minor. Tribes now considered 'Celtic' include the Helvetii in the area of what is now Switzerland, the Boii in what is now Italy, the Averni in what is now France, and the Scordisci in what is now Serbia. Nineteenth -century historians set great store by the supposed difference between 'Celtic' and 'Germanic' root-stocks, but modern research indicates that these were originally part of a common north European tradition, already differentiating into separate linguistic groups when they were geographically split apart by the Romans. We use the word 'Celtic' as shorthand for the indigenous peoples of north-west Europe who, apart from the Irish, were colonised by Rome and in all cases were cut off by the boundary of the Roman Empire from the 'German' tribes east of the Rhine and north of the Danube. 1
Celtic civilisation emerged around 700 BCE in Austria: the so-called Hallstatt culture. The wealth of Hallstatt was based on salt, which was traded for goods from Greece and Etruria. A development took place around 500 BCE in north-east France and the middle Rhine, the early La Tene period, after which the Celts became noticeably mobile. When they swept down into the Italian peninsula, they won the Po Valley from the Etruscans, founded Milan in the fifth century and sacked Rome in 390. They reached their widest area of influence in about 260, and were seen, together with the Persians and the Scythians, as one of the three great nations of barbarian Europe. During the seventh century the Celts arrived in Gaul, where from the third century onwards, under Roman influence, they took up a semisedentary life in towns, and began to act as merchants, travelling across Europe to buy, sell and often plunder goods. They had settled Britain in the sixth century BCE and at intervals thereafter, parts of Spain during the third century, and during the same century they colonised the Dalmatian coast
(part of what was until recently Yugoslavia), Thrace (modern Bulgaria) and parts of Asia Minor, where they became known as the Galatians. Strabo reported that the Celts were quarrelsome, brave, quick to fight, but otherwise not uncouth.2 Under the name of Gaesatae, they often worked as mercenaries, e.g. for Dionysius of Syracuse (Sicily) in the early fifth century, for the Macedonians, including Alexander the Great (336-323), and later for Hannibal (247-182).