In medieval castles, the area surrounded by a curtain wall, with or without towers, is known as the bailey. The outermost walls with their integrated bastions and wall towers together make up the enceinte or main defensive line enclosing the site.

The main defensive wall that encloses a castle is officially known as a Curtain Wall. This wall connects the various towers and gatehouses to create a continuous defensive perimeter, or enceinte. In many medieval designs, the curtain wall was topped with battlements (crenellations), which allowed defenders to fire arrows through gaps (crenels) while staying protected behind solid sections (merlons). A lower walkway on the inside of the wall is called the allure, or wall-walk. In more complex "concentric" castles, there are two layers: an outer curtain wall and a taller inner curtain wall, allowing defenders on the inner wall to fire over the heads of those on the outer wall. If the wall is a massive earthen embankment faced with stone, it may be referred to as a Rampart, but for the traditional stone structure seen in European fortifications, "Curtain Wall" is the standard architectural term.