French topographical draughtsman and engineer. He was born into the provincial gentry in Châlons-sur-Marne. Although the title that he assumed, Topographe du Roi, does not correspond to any known post of this period, that of Ingénieur du Roi did exist and designated a member of a corps created in the early 16th century that specialized in fortification, the art of besiegement and hydraulics. Chastillon is recorded in the service of Henry IV by 1595, when he received the relatively large sum of 1500 livres, evidence of the importance of the work he rendered in the civil war (1589) and the later frontier wars. He seems to have been a valued adviser of Henry IV's minister, the Duc de Sully, for he was entrusted with important civilian assignments: he produced an expert evaluation, in 1606, for the completion of the Cordouan lighthouse at the mouth of the Gironde River, a plan for a semicircular public place for the north-east entrance to Paris and a plan for a square in the new town of Henrichemont, Cher, the last a private development started by Sully. He also contributed to the building of the hospital in the Place des Vosges in Paris. //