How big were castles in the middle ages?
Castles varied from place to place. Much depended on their defences, where they were and what they were constructed with. Some were no more than Fortified Houses while others were entire communities offering defence for many. The main point of the defence was the Keep and of course the Gatehouse. There may or not be a moat, most often the castle is going to be on a hillside and will dominate its surroundings. irrespective of size the castle has to be self sufficient against a Siege, a starvation, by the enemy: Therefore its size will determine how resistable it is.
