The great natural features of a country so mountainous and intersected by so many arms of the sea as that of Scotland, seem at all times to have influenced its political divisions and the distribution of the various races in its occupation. The original territories of the savage tribes of Caledonia appear to have differed little from those of the petty kingdoms which succeeded them, and the latter as little from the subsequent provinces of the monarchy. The same great leading boundaries, the same natural defences, are throughout found occupying a similar position and exercising a similar influence upon the internal history of the country, while, amidst the numerous fluctuations and changes which affected the position of the northern tribes towards the southern and more civilised kingdoms of Britain, the two ever showed a tendency to settle down upon the great natural bulwarks of the south of Scotland as their mutual boundary, to which, indeed, the independent position of the northern monarchy in no slight degree owed its existence. Where the great arm of the western sea forming the Solway Firth contracts the island to a comparatively narrow breadth, not exceeding seventy miles, a natural boundary was thus partially formed, which had its influence at the very dawn of Scottish history; but, if during the occupation of the island by the Romans, who placed their trust more in the artificial protection of a rampart guarded by troops, the comparatively level ground in this contracted part of the country presented facilities for such a construction, the great physical bulwark of the Cheviot Hills had an irresistible attraction to fix the boundary eventually between the Solway and the Tweed, where that chain of hills extending between them proved so effectual a defence to the country along the whole of its range, that every hostile entrance into it was made either at the eastern or the western termination of that mountain chain. Farther north is the still more remarkable natural boundary where the Eastern and the Western Seas penetrate into the country in the Firths of Forth and Clyde, and approach within a comparatively short distance of each other, separating the northern from the southern regions of Scotland by an isthmus not exceeding thirty-five miles in breadth. This was remarked as early as the first Roman invasion of Scotland, when the historian Tacitus observes that these estuaries almost intersect the country, leaving only a narrow neck of land, and that the northern part formed, as it were, another island.[5]