The first French castles of the mediæval period seem to have been built for the purpose of arresting invasion and affording shelter to communities decimated by the raids of the Normans. They consisted of simple intrenchments more or less extensive. Surrounded by a _fossé_ or ditch formed of earthworks, the scarp of which was defended by a palisade, they had much in common with the camps of the ancient Romans. In the centre of the enclosure rose the _motte_ (mote or mound), a conical elevation, either natural to the ground, or artificially formed on the model of the Roman _prætorium_. This was surmounted by a building, generally of wood, which served as a post of observation and a retreat less accessible than the _enceinte_ itself. In these rudimentary dispositions we recognise the germ of those feudal keeps and castles which were such important features of mediæval architecture, notably during the Gothic period. [Illustration: 174. CASTLE OF ANGERS] Defensive works of this nature sprang up at various points of the royal domain which were exposed to the incursions of the Scandinavian pirates; but the temporary concessions of Charles the Bald were claimed as definitive by those to whom they had been made. "When, therefore, that feeble monarch proclaimed the heredity of the feofs at Quierzy-sur-Oise in 877, he did but sanction that which was already an accomplished fact.... When the feudal system was firmly established, the nobles turned their attention to the maintenance of their usurpations alike against the kings of France, strangers, and neighbours. To this end they carefully chose the best strategic positions in their territories, and fortified them in the most durable fashion at their command. The imposts they levied were considerable, and their serfs were subject to endless exactions."[65] Stone castles were accordingly built which, in general arrangement, adhered to primitive models. In 980 Frotaire had raised no less than five around Périgueux, his episcopal town. [65] Anthyme St. Paul, _Histoire Monumentale de la France_. In 991 Thibault File-Étoupe built a fortress on the hill of Montlhéry, near the royal residences of Paris and Étampes, which was very formidable to the first five kings of the house of Capet. Later, when it became a royal possession, it was one of the chief bulwarks of the city. [Illustration: 175. CARCASSONNE; CITADEL. VIEW FROM THE NORTH-EASTERN ANGLE. (SEE PLAN, FIG. 167)] In the Middle Ages the castle bore the same relation to the fortified town as did the keep to the feudal castle, and the history of one is bound up in that of the other. In a fortified town the castle was the lodging of the leader and his soldiers. It was connected with the ramparts of the place, and had one or more special outlets; it was further provided with defences on the side of the town itself, so that upon occasion it became an isolated stronghold.