Tower (or Keep) The tower is a circular or square building, which was used as a lookout and for defence. The central tower in a motte and bailey castle was known as the keep.

A castle's lookout is known by several names depending on its specific architectural function. The most common term is a Watchtower or Watch-tower, which is a standalone or integrated tower designed to provide a high vantage point for sentries. If the lookout is a small, projecting stone "window" or turret on the corner of a wall, it is called a Bartizan or Guérite. The narrow vertical slits in the walls that sentries look through (and shoot through) are called Embrasures or Arrow Loops. If you are referring to the high, fortified platform on top of a tower where a guard would pace, that is called the Wall-walk or Allure. In many medieval castles, the highest and most secure lookout point is the Keep or Donjon. Additionally, a small, elevated room on top of a tower specifically for a lookout is sometimes called a Turret. In 2026, when visiting historic sites in Europe, you may also hear the term Belvedere, though this is more commonly used for scenic lookouts in palace gardens rather than defensive military structures.