In basic terms, a castle need consist only of four thick walls with a door, some arrow-slits and a battlement. Indeed, some castles were little more than this. A water supply was vital, however, and there had to be space for the basic domestic requirements of the garrison and storage of essential supplies. However, castles of the Military Orders had to include additional elements that would allow their occupants to carry out a daily routine based on their monastic rule. Furthermore, the larger the castle and garrison and the more significant its strategic role, the greater the need for additional space for living quarters, protected training grounds, etc. It is not always easy to identify the use of a structure within a castle, although its location sometimes hints at the function, particularly so in castles which have a monastery-like layout. For example, a large hall located adjacent to a kitchen is most likely to have been the refectory and the presence of a latrine near a large room makes it probable that the latter served as the dormitory.