art which characterised the Iron Age Paganism of Scotland—Its difference from the art of the Christian time—Its special qualities and characteristics LECTURE IV. THE ARCHITECTURE OF THE BROCHS. The Broch of Mousa, Shetland—Its situation and Pages appearance—Its peculiarities of construction—Its 174–208 chambers, stairs, and galleries—Its features not related to those of any variety of castle of historic times—Many similar structures in different parts of Scotland—The Brochs of Glenelg—Broch at Loch Duich—Their typical plan—Evidence as to height—Typical characteristics of the Brochs—They point to a double intention in the minds of the builders—Their admirable adaptation for purposes of shelter and defence—Range or area of the typical form—Broch on Cockburn Law in Berwickshire—Broch at Torwood, Stirlingshire—Broch at Coldoch, Perthshire—Their numbers north of the Caledonian Valley—More than three hundred examples in the five northern counties—Significance of this result—They are the remains of a period of architectural activity which has no parallel in the history of the country—No example of the type is known except in Scotland—Instances of Brochs with peculiar features—Defensive works, wells, and drains—Construction of the doorway—The general adoption of such a peculiar system of strongholds points to the existence of peculiar circumstances in the history of the people—Uniformity of plan and construction a striking feature alike of the Round Towers of Ireland and the Brochs of Scotland—Dissimilarity of the two types of structure—Idea of which the Broch structure is the actual embodiment—The archæology of Scotland is largely composed of typical forms that occur nowhere else—Her monuments and metal-work demonstrate the existence of a National School of Decorative Art in Early Christian and Pagan times—The remains of these structures demonstrate the existence of a National School of Architecture as truly unique—Significance of these facts in relation to the unwritten history of Scotland LECTURE V. THE BROCHS AND THEIR CONTENTS.