Disturbed times of the high Middle Ages, from 400 to 1000, justify the construction of a fortress, out of wood at the beginning, then out of stone. These fortresses are called Castlings in country occitan. Close to the strategic points or obliged passages, they ensure on the one hand the safety and the incomes due to tolls sometimes even of the substantial ransoms which allow the richness of the lords and later of the city. From X° century, a village settles closest to the walls of the fortress which brings to the lords against safety, the labour and the reinforcement of the men-at-arms, the hamlet built on the slope is surrounded by a wall and makes use of the brook of Nègrerieu like ditch. Little by little, Brou is emptied until disappearing but leaves nevertheless the name to the city: Roquebrou.