According to Alfred Franklin in Les'rues et les cris de Paris au XIIIe siecle (1874), the streets of Paris were paved in the twelfth century because of a decree from the king

King Philip Augustus was staying at Paris, and was pacing around the royal hall meditating on the affairs of the kingdom. He came to the windows of the palace, where he liked sometimes to watch the river Seine to revive his spirit, but the horse-drawn carts that traveled through the city, churning up the mud, raised an intolerable stench. The king, pacing about in his hall, was unable to bear this, and he conceived of a very arduous but necessary plan, which none of his forebears had dared to approach because of the great difficulty and expense of the work. He called together the burgesses and provost of the...