The following is a brief timeline of the history of the "Celts", drawing on information from Brittania and other online resources.Overall TimelineBritish Isles and Cultures Referred To10,000 BCENeolithic (new stone age) Period beings in Europe.5000 BCENeolithic Period begins in British Isles; first evidence of farming appears; stone axes, antler combs, pottery in common use.4500-2500 BCEKurgan culture.4000 BCEConstruction of the "Sweet Track" (named for its discoverer, Ray Sweet) begun; many similar raised, wooden walkways were constructed at this time providing a way to traverse the low, boggy, swampy areas in the Somerset Levels, near Glastonbury; earliest-known camps or communities appear (i.e. Hembury, Devon).3500-3000 BCEFirst appearance of long barrows and chambered tombs; at Hambledon Hill (Dorset), the primitive burial rite known as "corpse exposure" was practiced, wherein bodies were left in the open air to decompose or be consumed by animals and birds.3000-2500 BCECastlerigg Stone Circle (Cumbria), one of Britain's earliest and most beautiful, begun; Pentre Ifan (Dyfed), a classic example of a chambered tomb, constructed; Bryn Celli Ddu (Anglesey), known as the "mound in the dark grove," begun, one of the finest examples of a "passage grave."2500 BCEBronze Age begins; multi-chambered tombs in use (i.e. West Kennet Long Barrow) first appearance of henge "monuments.; construction begun on Silbury Hill, Europe's largest prehistoric, man-made hill (132 ft).2500-1500 BCEMost stone circles in British Isles erected during this period; purpose of the circles is uncertain, although most experts speculate that they had either astronomical or ritual uses.2300 BCEConstruction begun on Britain's largest stone circle at Avebury.2300-1400 BCEBattle-Axe or Corded Ware culture; Beaker Folk identified by the pottery beakers (along with other objects found in their single burial sites).2000 BCEMetal objects are widely manufactured in England about this time, first from copper, then with arsenic and tin added; woven cloth appears in Britain, evidenced by findings of pins and cloth fasteners in graves; construction begun on Stonehenge's inner ring of bluestones.1800-1200 BCESecular control of society passes from priests to those who control the manufacture of metal objects.1500 BCEFarms (houses and separate, walled fields) in use on Dartmoor (Devon) and in uplands of Wales; stone circles seem to fall into disuse and decay around this time, perhaps due to a re-orientation of the society's religious attitudes and practices; burial mounds cease to be constructed; burials made near stone circles or in flat cemeteries.1500-1300 BCEÚnetice culture.1500-1200 BCETumulus culture.1300-700 BCEEmergence of a warrior class who now begins to take a central role in society. Some believe that these people, also known as the Urnfield civilization, are the "proto-Celts."1300 BCEProto-Celts arrive in Spain.1200 BCEProto - Celtic cultures in Gaul and Germania.1000 BCEEarliest hill-top earthworks ("hillforts") begin to appear, also fortified farmsteads; increasing sophistication of arts and crafts, particularly in decorative personal and animal ornamentation.750 BCEIron replaces bronze, Iron Age begins.600 BCENew Celtic invasion to Spain.600 BCEConstruction of Old Sarum begun.500 BCEEvidence of the spread of Celtic customs and artifacts across Britain; more and varied types of pottery in use, more characteristic decoration of jewelry. There was no known invasion of Britain by the Celts; they probably gradually infiltrated into British society through trade and other contact over a period of several hundred years; Druids, the intellectual class of the Celts (their own word for themselves, meaning "the hidden people"), begin a thousand year flourish.450 BCECeltic tribes come to Italy.280 BCECelts arrive to the Balkans and Asia Minor.150 BCEMetal coinage comes into use; widespread contact with continent.100 BCEFlourishing of Carn Euny (Cornwall), an Iron Age village with interlocking stone court-yard houses; community features a "fogou," an underground chamber used, possibly, for storage or defense.133 BCESpain conquered by Rome.50 BCEGaul conquered by Rome.43 CERomans conquer Britain.250 CEOgham inscriptions in Ireland and Scotland.409 CERomans leave Britain.450 CECeltic migrations to Brittany.844 CEKingdom of Scotland.In addition to the titles linked above, you may also find The Celtic World by Miranda Green and Europe: A History by Norman Davies, to be of interest.