In 1205 he acknowledged the feudal supremacy of the papacy and was crowned in Rome by Pope Innocent III, swearing to defend the Catholic faith (hence his epithet, "the Catholic").
I 1205 erkendte han pavedømmets overherredømme og blev kronet i Rom af pave Innocens 3. mod at sværge at forsvare den katolske tro (deraf hans tilnavn, "den katolske").