The reason why to the Greek mind, in the early centuries of history, the Celts appeared to occupy so much of Middle Europe and to occupy it so exclusively, was I think this: the Celts at that time actually occupied the upper valleys of the Danube, the Rhone, the Rhine, and the Elbe, and the high ground between. These rivers were the principal highways of such transcontinental commerce as then existed, and this commerce was probably considerable, comprising various metals, salt, amber, etc. Whatever came and went in the course of transcontinental trade from north-western Europe to the Mediterranean countries followed trade routes which lay through the central region north of the Alps, and all this region was held by the Celts. In this way, the Celts seem to be more extensively spread over northern middle Europe than they actually were. Archæology takes us back farther and tells us more than history in relation to the Celts while they were as yet, so far as we know, located solely or mainly in the mid-European region to the north of the Alps. It is not questioned that the ancient cemetery discovered and explored many years ago at Hallstatt in Upper Austria belonged to Celts and that the curious remains of art and industry found there are the work of a Celtic people. The period assigned for that work begins in the ninth century before the Christian Era and may extend onward for several centuries. The discoveries indicate an organised and progressive community, among whose resources were agriculture and the working of mines for metals and salt; but the principal fact disclosed is that, already in that early time, the Celts were acquainted with the use and manufacture of iron. In the northern parts of Europe, in Scandinavia, Britain and Ireland, as archæologists are agreed, the Iron Age did not make its appearance until several centuries later. We need not doubt that it was this possession of iron in abundance and of skill in its manufacture, at a time when neighbouring peoples found in bronze the highest class of material for their implements of industry and war, that gave the Celts the power and prosperity which they long enjoyed in Mid-Europe and enabled them to conquer and colonize all the countries that surrounded them. One effect of the mastery of iron, for a people occupying an inland region with small facilities for water-traffic, was that the Celts acquired a notable skill in the making of vehicles. From them in a later age the Romans borrowed the names of nearly every variety of wheeled vehicle that the Romans used: _carrus_ or _carrum_, _carpentum_, _esseda_, _rheda_, _petorritum_. From this it obviously follows that the Celts were also great road-makers. During the nine years that Julius Cæsar spent in the conquest of Transalpine Gaul, and marched his legions in every direction over that vast region, it is quite evident that he was operating in a country already well supplied with roads.