Iron Age Scotland is traditionally seen as part of the Celtic world. The area identifies itself today as Celtic, with features such as Celtic languages and place-names, the presence of what is termed Celtic art in the pre- and post-Roman periods. The Celts debate has a long pedigree in the country (Collis 2003). Earlier twentieth-century scholarship operated within a diffusionist paradigm, with a series of Celtic invasions from the Continent (see theme 2) Within this paradigm, later Celtic-language sources were readily treated as a 'window on the Iron Age' (Jackson 1964; c.f. Graham 1951; Hamilton 1968, 68-75). This pan-Celtic approach persists today, with Scottish material featuring in standard textbooks on Celtic religion and Celtic art (e.g. Green 1986; Megaw & Megaw 2001), and regularly displayed in exhibitions on the Celts (e.g. Moscati et al. 1991; Müller 2009).
The diffusionist / invasionist models came under heavy fire in the 1970s (e.g. Hodson 1960, 1964), while the 1990s saw a strong reaction against such pan-Celtic views among some British scholars (e.g. Chapman 1992; Merriman 1987; James 1999; Collis 2003). This was partly a general reaction against the conflation of sources from a wide range of places and dates to create a single, generic picture, and partly from differences between the people of the British Iron Age (never directly called Celtic in ancient sources) and their Continental neighbours. The attack on the Celtic model has led to much more focus on the detailed regional archaeologies of the British Iron Age in their own terms, a valuable development but one which has perhaps led to the underplaying of clear links which do exist to the Continent.
The debate has also impacted across disciplines. The current generation of archaeologists are much more wary of using linguistic or literary references to sustain their arguments, but there are signs of a more careful and critical approach to such data, which are valuable if treated on their own merits. The 'Celtic' adjective in languages, history and archaeology refers to entirely different sets of evidence which only partially overlap - speakers of what are now called Celtic languages did not necessarily all use what is now referred to as Celtic art or live in areas identified by the classical writers as Celtic. Yet this new, critical engagement between disciplines is starting to raise some interesting theories, such as recent work suggesting that the origins of what are called Celtic languages lie not in central or eastern Europe but in western Europe, with their spread linked to archaeologically-attested Bronze Age phenomena such as Beakers and the Atlantic late Bronze Age (see papers in Cunliffe & Koch 2010). This debate has a long way to run, but it suggests that now the worst excesses of the pan-Celtic gloss can be recognised and avoided, a more useful engagement between disciplines can begin.
Conditions are emerging for a more informed and critical dialogue between the different disciplines which are interested in Celtic studies; such interdisciplinary work has considerable potential, but requires a good appreciation of the limitations of the various sources of evidence.