The Full Story
Simon de Montfort was a rebel. In 1264, he led a baronial revolt against King Henry III, defeating and capturing the king at the Battle of Lewes. For the next year, de Montfort effectively ruled England.
In January 1265, he summoned a parliament. This wasn't unusual. Kings had summoned parliaments before. What was unprecedented was who de Montfort invited: not just barons and bishops, but two knights from every shire and two burgesses from the major towns.
It is the first known parliament in which ordinary townsmen, or at least property-owning commoners, sat alongside the knights of the shires.
De Montfort's parliament didn't last. By August 1265, he was dead, killed at the Battle of Evesham by forces loyal to the future Edward I. But the precedent survived. When Edward I called his 'Model Parliament' in 1295, he followed de Montfort's template: lords, clergy, and commons.
From this evolved the House of Commons, the idea that the people, through their representatives, should have a say in how they're governed. De Montfort lost the battle. His idea won.
Why This Matters
De Montfort's parliament created the template for representative government. The House of Commons, the most powerful chamber in British government, traces its origins to a rebel's experiment in 1265.