A gatehouse is a feature of European castles, manor houses and mansions. Originally a gatehouse was a fortified structure built over the gateway to a city or castle. In architectural terminology, a gatehouse is a building, enclosing or accompanying a gateway for a castle, manor house, or similar buildings of importance.
Gatehouses made their first appearance in the early Middle Ages when it became necessary to protect the main entrance to a castle or town. Over time, they evolved into very complicated structures with many lines of defense. Strongly fortified gatehouses would normally include a drawbridge, one or more portcullises, machicolations, arrow loops and possibly even murder-holes where stones or hot liquid would be dropped on attackers. In the late Middle Ages, some of these arrow loops might have been converted into gun loops (or gun ports).
Sometimes gatehouses formed part of town fortifications, perhaps defending the passage of a bridge across a river or a moat, as Monnow Bridge in Monmouth. York has four important gatehouses (such as the Micklegate) and known as Bars in its city walls.
The French term for gatehouse is logis-porche. This could be a large, complex structure that served both as a gateway and lodging or it could have been composed of a gateway through an enclosing wall. A very large gatehouse might be called a châtelet (small castle).
At the end of the Middle Ages, many gatehouses in England and France were converted into beautiful, grand entrance structures to manor houses or estates. Many of them became a separate feature free-standing or attached to the manor or mansion only by an enclosing wall. By this time the gatehouse had lost its defensive purpose and had become more of a monumental structure designed to harmonize with the manor or mansion.