 John met the rebel barons at Runnymede , and on 19 June 1215 they renewed their vows of fealty . A peace treaty , which later became known as Magna Carta , was sealed . Shortly after the treaty the agreement between John and Langton to appoint a royal constable in charge of Rochester Castle was dissolved , returning control to the archbishop . The peace did not last and the First Barons ' War broke out . A group of rebels headed to Rochester to hold the city against John . The events surrounding the rebels ' takeover of the castle are unclear , but contemporary chronicler Ralph of Coggeshall recorded that the king demanded Langton hand over the castle to royal control and the archbishop refused . Although Langton held out against the king 's demands , the rebels feared he would eventually cave to pressure from the king and seized control of Rochester Castle for themselves . According to Ralph of Coggeshall , this was done with the consent of the castle 's constable , Reginald de Cornhill , who seems to have switched allegiance from the king to the archbishop after John appointed him as royal constable of the castle . Langton left the country that same month , leaving the castle in the hands of the king 's enemies . In a letter that year to justiciar Hubert de Burgh John expressed his anger towards Langton , calling him " a notorious traitor to us , since he did not render our castle of Rochester to us in our so great need . " After this point , Rochester Castle was no longer considered to be in the perpetual custody of the archbishops of Canterbury . 
