The Celts (usually pronounced pron.: // but sometimes //, see pronunciation of Celtic) or Kelts were an ethno-linguistic group of tribal societies in Iron Age and Medieval Europe who spoke Celtic languages and had a similar culture, although the relationship between the ethnic, linguistic and cultural elements remains uncertain and controversial.
The earliest archaeological culture that may justifiably be considered as Proto-Celtic is the Late Bronze Age Urnfield culture of central Europe from the last quarter of the second millennium BC. Their fully Celtic descendants in central Europe were the people of the Iron Age Hallstatt culture (c. 800-450 BC) named for the rich grave finds in Hallstatt, Austria. By the later La Tène period (c. 450 BC up to the Roman conquest), this Celtic culture had expanded over a wide range of regions, whether 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 and Gallaeci) and northern Italy (Golaseccans and Cisalpine Gauls) and following the Gallic invasion of the Balkans in 279 BC as far east as central Anatolia (Galatians).
In recent years, tentative evidence has been adduced for a Celtic language in the Tartessian inscriptions of south Portugal and southwest Spain (dating 7th-5th centuries BC). Up until then, the earliest direct examples of a Celtic language had been the Lepontic inscriptions, beginning from the 6th century BC.Continental Celtic languages are attested only in inscriptions and place-names. Insular Celtic is attested from about the 4th century in ogham inscriptions, although it is clearly much earlier. Literary tradition begins with Old Irish from about the 8th century. Coherent texts of Early Irish literature, such as the Táin Bó Cúailnge (The Cattle Raid of Cooley), survive in 12th-century recensions.