Later during the Middle Ages, this basic formula was extended to include service rooms on the ground floor with, perhaps, a solar (private room for the lord and his family) on the first floor. Gradually these houses changed from a single unit, to a 'T' or 'L' shaped plan by the addition of a service range. Eventually they became much more sophisticated, developing into 'H' or 'E' shaped houses, or courtyard arrangements. Other types of manor house included 'castles' which, in their simplest form, were merely a defended residence of the lord.