Why did parliament split up into two groups during the Middle Ages?

Edward Ill came to the throne in 1327, and from that point, the representatives of the counties who were called the knights of the shire and of the towns who were the burgesses, became a permanent part of parliament.

When parliament opened, the Chancellor would explain to all the members why they had been summoned. The parliament would then split up. The Lords and important church officials would meet with the king and his council in the council chamber, while the lower clergy, knights, and elected representatives of towns and counties or burgesses would meet in another place. Both groups would discuss the royal requests separately, and then meet again to make their speeches.

Thus, two distinct houses of parliament emerged by the 14th century. One was composed of the elected representatives of the towns and counties. This became known as the Lower House, or House of Commons. The other was composed of religious leaders and nobility. This was the House of Lords, or Upper House. There is no doubt that the early parliaments were dominated by the king and his council, and the role of the House Commons was limited to presenting petitions.