On this day in 1229, Emperor Frederick II showed the crown in Jerusalem.
The city of Jerusalem had been won for Latin Christendom by Godfrey of Bouillon and the crusading army in 1099. Until its capture by Saladin in 1187, it had been the capital of a new, Latin kingdom in the Levant. Whilst the Third Crusade had shored up the Kingdom of Jerusalem, Richard the Lionheart did not even attempt to re-take the city. Thus the Kingdom of Jerusalem struggled on, a thin strip of land clinging to the east coast of the Mediterranean, perpetually in search of a king.
The young Frederick II, son of Emperor Henry VI, was heralded as the "Wonder of the World". Inheriting the (rather new) throne of Sicily, he was crowned king of Germany days before his 18th birthday, and went on collecting crowns to become king of Italy, Holy Roman Emperor, and king of Jerusalem.
At the time of Frederick's election to the german kingship, he had vowed to go on crusade, a vow he probably regretted. The realm of a Holy Roman Emperor was vast, heterogenous, and unruly. It had taken his illustrious grandfather, Frederick Barbarossa, decades to beat his empire into sufficient shape that he could go on crusade. But the younger Frederick had the eyes of the world on him, and he was expected to act quickly. As a child he had been a ward of Pope Innocent III, and was taught by the future Pope Honorius III, who would -- in time -- arrange his marriage to Yolande of Jerusalem. But the longer Frederick took to leave on crusade, the worse relations with the papacy became. Frederick married Yolande in 1225, but by 1228, when he finally left for Holy Land, he had been excommunicated by the new pope, Gregory IX.
Nevertheless, to his new kingdom he went, and in 1229 signed a remarkable treaty with the sultan Al-Kamil. The city of Jerusalem, and other towns including Bethlehem and Nazareth were returned to the Latin kingdom. On the 18th of March, Frederick went to the Church of Holy Sepulchre and placed the Imperial crown on his head. Finally, a Holy Roman Emperor had come to Jerusalem.
Frederick's bloodless recovery of Jerusalem impressed no one. What kind of "crusade" doesn't involve killing people?! Frederick was personally brilliant, but the Kingdom of Jerusalem had its own rules and traditions -- very different to those of Sicily -- to which he totally failed to adapt. A speaker of Arabic, curious by nature and cosmopolitan in outlook, he even failed to impress the muslims: he knew far too much about Islamic culture, which made people suspicious. Not only was he a Christian, he didn't even seem to be a very good Christian! And to the ecclesiastical community, an excommunicate going on crusade was simply a provocation.
Fortunately for everyone, Frederick was soon forced to leave. His father-in-law, John of Brienne (previous king of Jerusalem) had invaded Italy at the head of a papal army. An emperor's work is never done.