Today is being celebrated as the 750th anniversary of the first meeting of an English parliament that included the Commons - Parliaments had already met earlier in the reign of King Henry III, but had been more like the later Great Councils, consisting of the nobles alone gathered around the monarch to give advice and consent.
The 1265 Parliament was essentially called by Simon de Montfort, Earl ofc Leicester and brother-in-law to the King, who had been in his power since the Battle of Lewes the previous year. Earl Simon may well have thought having representitives of the knights of the shire and the towns would strngthen his regime, which was to collapse at the Battle of Evesham in August 1265. However the idea was not new - that noted constitional innovator and reformer King John had had a similar plan in 1212, even if the assenbley never actually met.
Most meetings of the Commons were in the Chapter House of Westminster Abbey until the mid-sixteenth century,when the Commons were given the Chapel of St Stephen in the palace of Westminster for their meetings in 1547.
The Chapter House of Westminster Abbey
Some of the glass dates from Sir George Gilbert Scott's restoration 1866-72, which revealed medieval encaustic floor tiles in excellent condition. On the walls are early fifteenth century paintings, including a scene of the Last Judgement.