The earliest history of the Celts is subject to uncertainty since they left no written records. Most of what we know is derived from archeological discoveries and the commentaries of Greek and Roman writers. The latter describe a tall, fair, muscular people, boisterous, warlike, energetic and restless. They were at once hospitable and quarrelsome, fond of drinking, feasting and story telling and of jewelry and bright colors. They were organized into extended families or clans, each with its own chieftain and local area of influence. These descriptions are doubtless too general, since the Celts, as as defined by a common root language, were not a single racial group. Their great weakness was their inability to form permanent alliances between clans, which ultimately lead to their defeat by the united power of the Romans and later, by the Anglo-Normans in England.

The Celtic people probably emerged around 1000 BC in the area which is now southern Germany. They seem to have been an amalgam of local barbarian tribes, Eurasians, and hunter-herders from the Black Sea area (perhaps Scythians). Celtic artefacts from a site at Hallstatt, Austria dated in the 8th century BC show the first stage of Celtic culture. These include jewelry, vessels and the spoked wheel. Many scholars believe that the Celtic language had also developed by this time. By the 7th century BC, they had become proficiant at working iron, and their superior weapons (compared to bronze) allowed them to spread rapidly over southern Europe, the coast of Britain, and possibly into the near east. A site at La Tene, Switzerland, dated around the later part of the 6th century BC contains artefacts from the second stage of Celtic culture, including jewelry, weapons and chariots. By this time, the Celtic language had almost certainly developed. From the 5th through the 3rd century BC, the Celtic empire dominated Southwestern Europe, made raids into Greece and Italy, and established an outpost in Turkey at Galatia. Around the beginning of the 4th century BC, Celts began to occupy southern England and Ireland, where they displaced or conquered earlier populations. From the 2nd century BC on, the Celts were subjected to increasing pressure from the Romans and Teutonic tribes. The Celts were steadily forced to the west and Britain. Their last continental stronghold was in the Brittany area of northwest Gaul. There, Julius Caesar's defeat of the Celtic chieftain Vercingitorix in 52 BC marked the end of Celtic power on the continent.

In the time of Caesar, the main peoples in the British Isles were identified by Classical scholars as Gaels and possibly Picts in Ireland, Picts and Caledonians in Scotland, and Britons (Brythons) in England and Wales. All of these were Celts except for the Picts, a shadowy people sometimes considered pre-Celtic. Over the first 3 centuries AD, the Romans conquered the South and East of Britain. Roman armies made repeated forays into Caledonia (Northern Scotland) but were never able to establish themselves permanently. The collapse of the Roman Empire in the 4th and 5th centuries AD provided other peoples the chance to expand. Picts and Scotti from Ireland raided and settled the west coast of Scotland and England. Britons invaded and settled Brittany (Armorica) in Gaul, from which the Celts had earlier been forced by the Romans. During the same period, Germanic peoples (Jutes, Saxons and Angels) from North Europe invaded Southern England, forcing the Celts back into the modern areas of Wales and Cornwall. From the 7th through the 9th century, Viking raiders ravaged the coasts of Northeast England, Scotland, Ireland and the Isle of Mann; they established many semi-permanent settlements and occasionally made alliances with local tribes. In Scotland, the Scotti and Picts united in 843 and drove the raiders out. The Vikings were finally defeated and expelled from Ireland in 1014 at the battle of Clontarf. In England, the struggle between the Saxons and the Norse settlements continued until after 1000, when a united Anglo-Danish state was finally achieved. In 1066, the Normans invaded England. Over the course of the next 600 years, they formed the current English state and conquered the Celtic nations of Ireland, Scotland and Wales. In the 20th century have these latter have started to win their independence. With that has come a renewed interest in a proud and ancient heritage which has somehow survived to enrich our own lives.