Why did Frederick II crown himself king of Jerusalem?

Frederick II crowned himself king of Jerusalem on March 18, 1229, in the Church of the Holy Sepulchre as a definitive expression of his conception of sovereignty.1

His claim to the throne was rooted in his marriage to Isabella (Yolande) of Brienne, the heiress to the kingdom of Jerusalem. Following her death in 1228, Frederick asserted his right to the regency for their infant son, and his self-coronation served to solidify his authority as a ruler.21

This act occurred during the Sixth Crusade, a campaign he undertook while under the ban of excommunication by Pope Gregory IX. By crowning himself—with a Teutonic Knight reading the ceremony in the absence of clergy due to an interdict—Frederick signaled his belief in his own messianic role, comparing his entry into the city to that of Christ on Palm Sunday. This moment represented both the high point and a turning point in his imperial design, as he viewed himself as a new David.231