 The exact geographic spread of the ancient Celts is disputed; in particular, the ways in which the Iron Age inhabitants of Great Britain and Ireland should be regarded as Celts have become a subject of controversy.According to one theory, the common root of the Celtic languages, the Proto-Celtic language, arose in the Late Bronze Age Urnfield culture of Central Europe, which flourished from around 1200 BC.According to another 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.