This paper focuses on a unique and yet overlooked source which offers an interesting insight into the daily life of a late-medieval Italian castle during a time of war. It is a list of the guards as well as the other defenders of the castle of Collalto (north of Treviso) from 1373, which also contains a set of rules for them. After a short introduction to the history of the Collalto family and a description of the source, the author offers some theories as to what circumstances and motives may have led the lord of the castle, Count Rambaldo IX di Collalto, to drawing up the document in question. Subsequently, the source is used to analyse the social structure of the garrison and the defence system of the castle of Collalto.