 Henry IV then disbanded and released his army as father and son left for the diet in Mainz on December 21.On December 23 in Bingen, Henry persuaded his father to retreat to a castle for his own protection, as Archbishop Ruthard of Mainz would refuse to let him into the city.Henry agreed and was led to Böckelheim Castle, the property of Bishop Gebhard, not for his protection, but for custody.