An elaborate scenario founded the scientific aim of the construction project of a fortified castle in Guédelon. It all started with the story of a small lord of Puisaye, badly dwelt between a powerful suzerain and prosperous abbeys, who, under the reign of Louis IX, undertook to endow his lineage with a fortified castle to materialize his power. The fortress was placed at the break of the plateau bearing the forest of Boutissaint and the fiefdom of Ratilly. The master tower was oriented facing the slope to monitor the valley of the pond of Guédelon, a local toponym. The site was installed in the forest to allow the clearing and harvesting of firewood for lime, on a slight rise for monitoring, and directly in the ferruginous sandstone quarry to reduce costs. In addition, Puisaye sandstone resists frost well and, by its compactness, prevents the rise of moisture from the ground in the walls, two considerable qualities in a humid region with harsh winters.