In the fourteenth century military architecture developed chiefly on reconstructive lines. Ancient fortresses were reorganised in accordance with the new methods of attack and (consequently) of defence, and the weak points brought to light by recent sieges were dealt with. The same process was applied to the construction of towers which had hitherto been furnished with several rows of loopholes, an excellent expedient for the defence of curtains and approaches, but subject to this drawback, that it directed attention to the most vulnerable points. The first effect of the use of cannon in warfare was to increase the thickness of the walls; subsequently, such structural modifications were adopted as were required by the novel method of massing all the defences at the summit of machicolated walls. The principal castles of this period were Vincennes, near Paris, built by Philip of Valois and Charles V., and the vast fortified palace at Avignon, constructed by the Popes Benedict XII., Clement VI., Innocent VI., and Urban V., of which we shall have more to say in Part IV. Gaston Phœbus, Count of Foix and Béarn, built square keeps in the _Bastide_ of Béarn, at Montaner, and at Mauvezin, besides circular keeps at Lourdes and at Foix. [Illustration: 184. CASTLE OF TARASCON] Among keeps and castles completed or entirely built in the fourteenth century, Anthyme St. Paul enumerates those of Roquetaillade, Bourdeilles, Polignac, Briquebec, Hardelot, Rambures, Lavardin (the foundations of which were laid in the twelfth century), Montrond, Turenne, Billy, Murat, and Hérisson, the curious keep of Montbard, the keeps of Romefort, Pouzauges, Noirmoutier, and many others. At the end of the fourteenth and beginning of the fifteenth century Louis of Orleans, son of Charles V., took advantage of the madness of his brother Charles VI. to fortify various positions on which he relied for the furtherance of his ambitious schemes. In 1393 and the years immediately following he acquired various estates in Valois: Montépilloy, Pierrefonds, and La Ferté-Milon, the castle of which he rebuilt entirely. He also bought the domain of Coucy in 1400, after the death of the last male descendant of Enguerrand III. Coucy, Pierrefonds, and La Ferté-Milon have been so exhaustively described in special works, notably those of Viollet-le-Duc, that we need not reproduce them here. We have cited them as characteristic types of those colossal fortresses and keeps, admirable alike in grandiose proportion and refinement of detail which are the supreme expression of feudal power. [Illustration: 185. VITRÉ CASTLE] Several other castles were built in Albigeois, Auvergne, Limousin, Guyenne, La Vendée, and Provence, notably at Tarascon. The keeps of Trèves in Anjou also date from this period. Important castles sprang up all over Brittany in the fifteenth century. Such were Combourg, Fougères, Montauban, St. Malo, Vitré, Elven, Sucinio, Dinan, Tonquédec, etc.