There is, then, no evidence from archæology, history, or language, sufficient to establish even a moderate degree of probability for the theory of a Celtic occupation of Ireland or Britain during the Bronze Age.

On the other hand, taking Coffey's approximate date of 350 B.C. as the beginning of the period of the general use of iron in Ireland, we shall, I think, find sufficient evidence to warrant the belief that the Celts reached Britain and Ireland about that time, and not earlier, at all events not considerably earlier than that time.

Why not earlier? I think we have conclusive grounds for believing that the Celtic migrations to Ireland cannot have begun very much, if at all, sooner than the fourth century B.C. Before stating these grounds, let us ask is there any discoverable reason for supposing that the Gaels inhabited Ireland from a time many centuries farther back. I think it possible that those who in modern times have entertained this view have been influenced by the dates assigned to the Gaelic immigration by Irish writers like the Four Masters and Keating. These dates may be taken to correspond closely enough with the estimates of archæological authorities for the commencement of the insular Bronze Age, and, in the absence of evidence to the contrary, it might be imagined that they were founded on some basis of tradition.

It is not the habit of popular tradition to encumber itself with chronology. There is no known instance of ancient reckoning in years and periods of years that is not based on some era, on the accepted date of some real or supposed event or events. Nowhere in Irish tradition has any trace been found of the existence of a native system of chronology before the introduction of Christian learning. In a paper published in the Proceedings of the Royal Irish Academy (July, 1910), I have shown how the extant written chronology of the Irish Invasions was first originated. The method was not unlike Sir John Rhys's series of equations.

The Irish historian found in Latin histories a set of definite epochs by which antiquity was divided: the beginning of the Assyrian empire, the beginning of the Median empire, the beginning of the Persian empire, the usurpation of the Magi in Persia, and the beginning of Alexander's empire. The chronology of the Irish Invasions was settled by the easy process of making each invasion coincide exactly in time with each of these epochs. It is evident that no traditional value can be attached to a chronological system of this kind.

But, it may be objected, the very remoteness of the time assigned to the Gaelic invasion by Irish historians may reflect the popular belief in its remoteness. If that be so, then the earlier the historian is the more near he is to the popular tradition. In the paper just cited, I have shown that, in the earliest known version of this chronology of the Invasions, the Gaelic migration to Ireland coincides with the date of Alexander's empire, 331 B.C. That is not very far from the date assigned by Coffey for the end of the Bronze Age in Ireland, about 350 B.C. For my own part, I attach no traditional value to this coincidence, but if it pleases anyone to insist that Irish prehistoric chronology has a traditional value, then it must be conceded that tradition, as far as it is valid, is altogether favourable to the view that the Gaelic occupation of Ireland belongs to the end, and not to the beginning, of the Bronze Age.

The migratory movements of the Celts on the Continent have a bearing which cannot be ignored on the time of the Celtic migrations to Britain and Ireland. So far as I am aware, no modern investigator has suggested that the Celts were not already in the Iron Age at the time of their expansion into Italy and Spain. Why then should it be imagined, in the absence of any positive indication to the purpose, that they occupied these islands more than a thousand years earlier?

If I am not mistaken, the archæological evidence is fairly decisive on the point. Archæologists are agreed in dividing the Celtic Iron Age into two main periods, the Early Celtic or Hallstatt period, and the Late Celtic or La Tène period, also called the Marnian period. Each of these periods is taken to consist roundly of about four centuries, and the two periods on the Continent together correspond roughly to the last eight or nine centuries before the Christian Era. The Late Celtic period is abundantly represented in the antiquities of Great Britain and Ireland, but the objects that have been found in either country belonging to the Early Celtic Period are extremely rare. On this head Coffey writes as follows ("Bronze Age in Ireland," page 5):

"It must be remembered that the Continental Hallstatt period is not at present well represented in Great Britain and Ireland, and though, under Hallstatt influence, certain Continental Iron-Age types such as bronze caldrons, trumpets, round shields, etc., found their way into Ireland, we cannot as yet definitely separate this period from the end of the Bronze Age."