Modern Ireland is habitually referred to as a Celtic country, and it is generally taken for granted that this distinctive identity derives at least in part from incursions by prehistoric Celtic people. Addressing the question of Celtic migrations into Ireland involves teasing apart the major components that contribute to our modern concept of the ancient Celts (the classical literature, language, and material culture), each of which provides an alternative definition of Celticness. In the past it has proved tempting to combine these definitions, invoking the notion of a culturally unified Celtic people in prehistory. As part of their migratory spread, these Celts were thought to have established themselves in Ireland, introducing the ancestral form of the Irish language. This idea of prehistoric Celtic colonialism was further bolstered by the accounts of successive migrations into Ireland presented in early Irish documents such as the Lebor Gabála Érenn (Book of invasions), a medieval amalgam of myth and pseudohistory. Although population movement undoubtedly played a part in the emergence of Ireland's Celtic identity, the full picture is likely to be rather more complex.
The Classical Celts
It is clear from the writings of the classical authors that the Mediterranean world was rocked to its foundations during the fourth and third centuries b.c.e. by the belligerent attentions of migratory bands known as Keltoi (to the Greeks) or Celtae (to the Romans). Sweeping south across the Alps, these tribal groups, linked in loose confederacies, enjoyed a series of remarkable successes. Rome itself was sacked in 390 b.c.e., and Celtic settlements were established in northern Italy, across much of eastern Europe, and as far east as Asia Minor. The tide eventually turned, however, and the expansion of Roman control in the second and first centuries b.c.e. led eventually to the virtual extinction of continental Celtic culture.
No classical source refers to the presence of Keltoi or Celtae in Ireland. Indeed, Caesar makes an explicit statement in his Gallic Wars that the Celtae were just one of three ethnic groupings in Gaul (modern France). His near-contemporary Strabo explicitly states that Ireland lies beyond "Celtica." In this rather limited sense, then, there was no prehistoric Celtic population in Ireland.
It was the linguistic definition of a "Celtic" language family, linking living languages such as Irish and Scots Gaelic, Welsh, Cornish, and Breton to vanished tongues such as ancient Gaulish, that first saw the term Celtic applied to Ireland. This language family was defined in the first decade of the eighteenth century by the Welsh polymath Edward Lhuyd, building on the work of the Breton scholar Paul-Yves Pezron. Similarities of grammar and vocabulary demonstrate that Irish is a descendant of languages spoken widely across Europe during the Iron Age. This is, however, a much looser use of the term Celtic than that applied by Caesar and the other classical authors.
The earliest evidence for the existence of Celtic languages in Ireland is contained in a series of fragmentary and ambiguous classical texts. A lost sailing manual that may date from before 500 b.c.e. seemingly calls the Irish by the Celtic name Hiernii. As the relevant text survives only in a much later poem, however, the reference may be misleading. Indeed, the first secure written source is Caesar, who described the island of "Hibernia" in his mid-first-century b.c.e.Gallic War. By the second century c.e. the Greek geographer Ptolemy was able to list more than fifty tribal groups and places with Celtic names. Clearly, therefore, Ireland was Celtic-speaking by the period of Roman influence, and possibly many centuries earlier.
Archaeology and the Celts
In order to identify the nature and extent of any prehistoric migrations that may have introduced Celtic languages into Ireland, we have to rely on the evidence of archaeology. Since the middle of the nineteenth century archaeologists have identified the Celtae of classical literature with the distinctive Iron Age art style known as La Tène. This exuberant art style, dominated by abstract curvilinear patterns usually applied to aristocratic paraphernalia such as weaponry, personal adornment, and religious objects, seems to have originated in the indigenous Iron Age (Hallstatt) communities of central Europe around 450 b.c.e. The appearance of distinctive La Tène material in migration-period cemeteries in northern Italy confirmed that the bearers of La Tène art formed at least one group among the classically attested Celtae.
Over a period of some 200 years La Tène art spread both north and west, making its first appearance in Ireland some time around 300 b.c.e. (although the majority of the objects are from several centuries later). The arrival of this alien art style has been widely accepted as evidence of further Celtic incursions into areas where no literate commentators were available to record their actions. Unfortunately for proponents of the invasion hypothesis, La Tène objects in Ireland are quite distinct in form and character from those of the continent, and actual imports are exceptionally rare. Equally problematically, La Tène material in Ireland is highly localized and concentrated in the northern half of the island, and is all but restricted to objects associated with the military or religious elite. Although the ideas embodied in La Tène art were clearly imported, their execution was overwhelmingly native in character. It is hard, therefore, to maintain that there was ever any La Tène migration into Ireland beyond a trickle of warriors and craftsmen. It seems improbable that such limited incursions could have so rapidly transformed the linguistic map of the whole island.
Some commentators, recognizing the inadequacy of the La Tène period as a point of origin for Celtic Ireland, have suggested that the migration of Celtic speakers may have occurred earlier. Continental archaeologists are agreed that the makers of La Tène art were the descendants of central European Hallstatt communities, and some distinctive Hallstatt material does occur in Ireland in the seventh century b.c.e. Hallstatt material in Ireland, however, is largely restricted to bronze swords deposited in rivers, most probably as part of ritual performance. As with the later La Tène material, these swords appear to be locally made, and their riverine deposition is similar to that of earlier bronze weaponry in Ireland. In terms of the broader linguistic picture, the seventh century b.c.e. would be a convenient "window of opportunity" for the introduction of Celtic languages to Ireland. The archaeological evidence, however, is extremely slight.
If the adoption of these exotic forms of material culture do not represent Celtic migrations, how then did Celtic languages come to be spoken in Ireland? An alternative view has been propounded recently which suggests that, rather than arriving in Ireland fully formed, Celtic languages evolved across a wide area of western Europe, including Ireland, as a by-product of the intense trading activities of the Late Bronze Age (around 1200–700 b.c.e.). Proponents of this view suggest that early forms of Celtic emerged as common trading languages to facilitate communication between people whose first languages were mutually unintelligible. Because of their association with the prestigious bronze trade, these early Celtic languages may have been adopted first by the social elite and ultimately by the lower orders through a process of social emulation. In this way, like the later language diffusions associated with Swahili and Malay, Celtic languages might have been widely disseminated without the need for actual population movement on any numerically significant scale.
It remains entirely possible, of course, that there may have been substantial movements of population that left no archaeological traces. Many periods are not characterized by archaeologically distinctive material, and it would be naïve to suppose that every event of significance in prehistory should leave an archaeological signature. Nonetheless, the wholesale migration of prehistoric Celtic peoples into Ireland seems improbable, and a more diffuse pattern of smaller-scale movements by high-status individuals, families, craftsmen, war bands, and other collectives seems a more likely mechanism for the emergence of Irish Celtic identity.
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Mallory, James. P., and Thomas E. McNeill. The Archaeology of Ulster: From Colonization to Plantation. 1991.
Raftery, Barry. La Tène in Ireland: Problems of Origin and Chronology. 1984.
Raftery, Barry. Pagan Celtic Ireland. 1994.