This fortress was built on one of those great blocks of slate which are found in abundance between Mayence and Dinan, scattered in all directions among the copses and along the heath like the missiles of some Titanic combat. The tower composed the entire fortress; and below the tower stood the rock at whose base flowed one of those water-courses which swells into a torrent in January and dries up in June. Simple as were its means of defence, this tower was almost impregnable in the Middle Ages, but the bridge had proved a source of weakness. The Gauvains of Gothic times had built it without a bridge. It was formerly accessible by means of one of those swinging bridges that could be instantly severed by the stroke of an axe. So long as the Gauvains remained Viscounts it pleased them just as it was, and they were satisfied with it. But when they became Marquises and exchanged the keep for the Court, they spanned the stream with three arches and thus offered access in the direction of the plain very much as they had yielded to the advances of the king. The marquises of the seventeenth century and the marchionesses of the seventeenth no longer prided themselves on their impregnability. They abandoned the traditions of their ancestors to follow the fashions of Versailles. Facing the tower towards the west was a somewhat elevated plateau adjoining two plains; this plateau was very near the tower, only separated from it by a deep ravine through which flowed a stream tributary to the Couesnon. The bridge that connected the fortress with the plateau stood on lofty piles, and on these piles was constructed as at Chenonceaux a building in the Mansard style of architecture, but more comfortable than the tower. Customs were still very rude, and the lords continued to occupy chambers in the keep that were more like dungeons than bedrooms. As to the building on the bridge, which was a diminutive kind of castle, a long corridor had been added to it, by way of entrance, which was called the hall of the guards. Over this hall, which was like an entresol, was the library, and above that a granary. Separated by pillars stood the long windows with their small panes of Bohemian glass; medallions were sculptured on the walls. The fortress was three stories high; halberds and muskets were to be found below, books in the middle, and over all the bags of oats,--a somewhat barbarous arrangement, but princely to the last degree. The tower loomed above this coquettish building presenting a stern and gloomy contrast. The platform offered a point of attack from which the bridge could be destroyed.