It’s the 14th of February, the year 1265, and something big is about to go down in the chapter house of Westminster Abbey. Parliament has already been in session for more than three weeks, long for parliaments of that era, and the agenda is dominated by one issue: what to do with the lord Edward, heir to the throne. It will be remembered how a disaffected group of barons and clergy under Simon de Montfort defeated forces loyal to King Henry III in the spring of 1264. They established a constitutional monarchy, with Edward and other male members of the royal family held hostage for the king’s good behavior. A complicated scheme of government has now been worked out for Edward’s release, and Montfort decides to have it proclaimed in the chapter house. This will be a bitter pill for Henry to swallow. It’s not just that he has to accept their plan or risk the imprisonment or banishment of Edward and his other son Edmund (father of the House of Lancaster), but the chapter house was his pet project, envisaged as the home for future parliaments, where the business of the realm would be discussed under his beneficent lordship. Such was its beauty that he inscribed it with the motto, ‘As the rose is the flower of flowers, so is this building the house of houses’. Now, that house belonged to Simon de Montfort and his party.