Where does the word castle come from? Strangely enough, medieval writers never made up a new word to describe this new building type. They continued to use Latin words like castrum (pl. castra) and castellum (castella), meaning a town, a walled enclosure, a stronghold, or sometimes simply a tower. Ancient Romans called any stronghold or walled place a castrum, and used the diminutive form, castellum, for everything from a fortress to a dwelling on a hill. Ancient Roman military camps with ditches and palisades, for example, were also called castra. In the early Middle Ages, authors used these words for any inhabited place. But meanings changed, and from a rather vague designation for any walled enclosure, “castle” came to mean a specific kind of building. By the eleventh century castellum had entered the vernacular languages of Europe as castle (English), castillo (Spanish), castello (Italian), or chateau (French), although burh, burg, borg, berg, or burgh remained the preferred form in Germanic languages.
As we use the word today, a castle is not a palace, which is unfortified, although a castle and a palace are both imposing residences. Nor is it a fort, for that word implies a purely military function and a garrison. Neither is a castle a walled city, although a royal castle may house as many people as a town, for the castle—even with all its buildings and inhabitants—has a single owner. In short, a castle combines a variety of building types in a new way, often using the same kind of sophisticated decoration and fine masonry to be found in religious architecture. A castle was a secure place to live and to administer the surrounding estate, and as a headquarters and court of justice, it became the visible symbol of its owner’s authority.