The Celts (/ˈkɛlts/, occasionally /ˈsɛlts/, see pronunciation of Celtic) were people in Iron Age and Medieval Europe who spoke Celtic languages and had cultural similarities,^[1] although the relationship between ethnic, linguistic and cultural factors in the Celtic world remains uncertain and controversial.^[2] The exact geographic spread of the ancient Celts is also disputed; in particular, the ways in which the Iron Age inhabitants of Great Britain and Ireland should be regarded as Celts has become a subject of controversy. The history of pre-Celtic Europe remains very uncertain. According to one theory, the common root of the Celtic languages, a language known as Proto-Celtic, arose in the Late Bronze Age Urnfield culture of Central Europe, which flourished from around 1200 BC.^[5] In addition, according to a theory proposed in the 19th century, the first people to adopt cultural characteristics regarded as Celtic were the people of the Iron Age Hallstatt culture in central Europe (c. 800–450 BC), named for the rich grave finds in Hallstatt, Austria.^[5][6] Thus this area is sometimes called the ‘Celtic homeland’. By or during the later La Tène period (c. 450 BC up to the Roman conquest), this Celtic culture was supposed to have expanded by diffusion or migration to the British Isles (Insular Celts), France and The Low Countries (Gauls), Bohemia, Poland and much of Central Europe, the Iberian Peninsula (Celtiberians, Celtici, Lusitanians and Gallaeci) and northern Italy (Golaseccans and Cisalpine Gauls)^[7] and, following the Gallic invasion of the Balkans in 279 BC, as far east as central Anatolia (Galatians). (Wikipedia.org)

A Druid (Old Irish: druí; Welsh: derwydd) was a member of the educated, professional class among the Celtic peoples of Gaul, Britain, Ireland, and possibly elsewhere during the Iron Age. The Druid class included law-speakers, poets and doctors, among other learned professions, although the best known among the Druids were the religious leaders. Very little is known about the ancient Druids. They left no written accounts of themselves, and the only evidence are a few descriptions left by Greek, Roman, and various scattered authors and artists, as well as stories created by later medieval Irish writers.^[2] While archaeological evidence has been uncovered pertaining to the religious practices of the Iron Age people, „not one single artefact or image has been unearthed that can undoubtedly be connected with the ancient Druids.”^[3] Various recurring themes emerge in a number of the Greco-Roman accounts of the Druids, including that they performed animal and even human sacrifice, believed in a form of reincarnation, and held a high position in Gaulish society. Next to nothing is known for certain about their cultic practice, except for the ritual of oak and mistletoe as described by Pliny the Elder. (Wikipedia.org)