As pope, Innocent III began with a very wide sense of his responsibility and of his authority. During Innocent III's reign, the papacy was at the height of its powers. He was considered to be the most powerful person in Europe at the time. In 1198, Innocent wrote to the prefect Acerbius and the nobles of Tuscany expressing his support of the medieval political theory of the sun and the moon. His papacy asserted the absolute spiritual authority of his office, while still respecting the temporal authority of kings.