The _Château Gaillard_, built at the close of the twelfth century on an eminence commanding the Seine at Les Andelys, has several peculiarities of arrangement. The round keep is first enclosed by a circular _enceinte_, or rather by a square, the angles of which have been rounded. This in its turn is surrounded by an elliptic enclosure connected with the defences of the castle, and consisting of a series of segmental towers united by very narrow curtains. In this massive structure the art of the architect manifests itself only in the robust solidity of the masonry. It is the keep in its purely military character. No trace of decoration mitigates its austerity. [Illustration: 181. CASTLE OF CHINON. SOUTH FRONT] Philip Augustus, having possessed himself of the Château Gaillard, fortified Gisors on the same formidable scale, and proceeded to build the castle of Dourdan as well as his own palace fortress of the Louvre, in Paris. Upon the death of the king, Enguerrand III. began to build a fortress at Coucy, which he completed in less than ten years (1223-1230). Its grandiose proportions and formidable system of defence surpassed everything that had gone before. Coucy was, in fact, the architectural manifestation of that haughty ambition to which Enguerrand is said to have given free expression during the minority of his sovereign. [Illustration: 182. CASTLE OF CLISSON. KEEP] Next in importance to the castles and keeps of the thirteenth century, already enumerated, are the following:--The White Tower of Issoudun; the Tower of Blandy; the octagonal keep of Châtillon-sur-Loing, Semur; the royal fortresses of Angers, built by St. Louis; Montargis, Boulogne, Chinon, and Saumur; the _Tour Constance_ or keep of Aigues-Mortes, ascribed to St. Louis; the castle of Najac, built by his brother, Alphonse of Poitiers; the castles of Bourbon l'Archambault and Chalusset, and the castle of Clisson, rebuilt or begun by Olivier I., Lord of Clisson, after his return from the Holy Land, etc. [Illustration: 183. VILLENEUVE-LES-AVIGNON. CASTLE OF ST. ANDRÉ]