Siege of Aachen (1248)

The Siege of Aachen, which lasted from late April or early May until October 1248, was part of the German civil war that began with Pope Gregory IX's proclamation of a crusade against the Emperor Frederick II in 1240. The city of Aachen, which was the traditional coronation site of German kings, supported Frederick II and refused to allow his rival, Count William II of Holland, to enter the city to be crowned. William and his supports besieged the city, forcing it to allow him in, where he was crowned German king.

The main primary sources for the siege are the Royal Chronicle of Cologne, the Chronicle of the Monastery of Bloemhof and Matthew of Paris's History of the English.

The crusade launched in 1240 was the second against Frederick II, a declared enemy of the church. The first crusade, also called the War of the Keys, lasted from 1228 until 1230, when Frederick and the papacy were reconciled and he was re-admitted to communion. In 1239, he was excommunicated a second time, and when he threatened to march on Rome Gregory IX proclaimed a crusade. In 1245, Pope Innocent IV declared Frederick deposed and the prince-electors loyal to the papacy elected Henry Raspe, the landgrave of Thuringia, as the new German king (to be crowned emperor at a later date by the pope). On 16 February 1247, Henry died and the electors chose William of Holland as his successor on 3 October 1247.

When the city of Aachen refused to allow William's supporters in, they began to surround it to besiege it in late April or early May. William was at Kaiserswerth as late as May 1 and may not have taken part in the opening of the siege. The siege opened with a skirmish by one of the city gates that left sixteen attackers and one defender dead. William had arrived with a large army by May 7, and Cardinal Pietro Capocci, the papal legate, arrived in the middle of May.

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