It was to Philippe-Auguste also that the city of Paris was indebted for its first paved streets. In 1185, five years before the wall of fortification was begun, he was in one of the great halls of his palace in the Cité, and approached a window whence he was in the habit of watching the traffic on the Seine. Some heavy wagons or carts were being drawn through the streets at the time, says the historian Rigord, and such an insupportable odor was stirred up from the mud and filth that the king was obliged to leave the window, and was even pursued by it into his palace. From this occurrence came his resolve to carry out a work from which all his predecessors had shrunk because of the great expense involved, and which, indeed, discouraged the bourgeois and the prevost of the city when the royal commands were laid upon them. Instead of carrying it out for all the streets and by-ways of the capital, they appear to have contented themselves with paving the environs of the palace, and the two streets which traversed the Cité from north to south and from east to west, and which were called the _croisée de Paris_. This paving was effected by means of square stones fifteen centimètres long and fifteen to eighteen thick. The bourgeoisie found the expense so heavy that under Louis XIII half of the streets of Paris were still unpaved. In 1204, the king charged the _prévôté_ of Paris to pay to the prior and the monks of Saint-Denis de la Chartre thirty sous parisis for the privilege of building on their land, and he commenced the construction of the Louvre. The site had long been occupied by a sort of suburban house of entertainment, and the king resolved to erect a strong château, commanding the Seine. This château was square, the thick walls pierced with small windows and loopholes arranged without order, surrounded by wide and deep ditches, and completed by a great tower rising in the middle. Over the pointed roof floated the royal banner, and within were confined the State prisoners, and the royal treasures, crown-jewels, and _Trésor des Chartres_. In 1200, this indefatigable monarch conceived the idea of uniting all the different schools established in Paris under one head, but the corporation of the Université was not constituted until twelve years later.