these only 2.5 million speak a Celtic language, as do, possibly, a further one million outside the Celtic areas.

Though writing was known to them, and used on funeral stones and pottery prior to the first century b.c., it was not until the Christian era that the change in religious perceptions allowed the Celts to shake off the old druidic prohibition against committing their store of knowledge to written form. It is from the sixth century a.d. that an extensive written testimony in the Celtic languages survives, including one of Europe’s oldest and most vibrant mythologies, which until the Christian period had been handed down in oral tradition.

First recorded by the Greeks as keltoi, perhaps from a native word meaning “hidden people,” by the Greek Hectaeus (ca. 517 b.c.), the Celts had already begun to migrate through Europe from their original homeland at the headwaters of the Danube, Rhine, and Rhône (all three rivers still carrying their Celtic names). It is thought that they were called “hidden people” because of the prohibition by their religion to commit anything to written record. The etymology of the word may well be the same root that gives us ceilt, an act of concealment, and kilt, the short male skirt of Celtic dress.

The Celts began their expansion through Europe around the start of the first millennium b.c., at which time they possessed great metalworking skills, especially in the use of iron (itself a Celtic word borrowed into the German languages, iarn). This metal was only just becoming known to craftsmen of the Classical world. With their iron weaponry and tools, the Celts were able to cut through the impenetrable forests of Europe.

By the sixth century b.c. they were established in France and Spain, as far south as Cadiz, and in the Po Valley of Northern Italy. It is believed that the Goidelic form of Celtic was the more archaic form and that it was Goidelic speakers who had settled in Spain, Ireland, and Britain by at latest the start of the first millennium b.c. Brythonic, or P Celtic, is regarded as a later modification of the Goidelic form.

It is believed that the two linguistic groups (Goidelic and Brythonic) diverged over 2,500 years ago. The Brythonic group began to simplify itself in its case endings and in the loss of the neuter