A gatehouse is a type of fortified gateway, an entry control point building, enclosing or accompanying a gateway for a town, religious house, castle, manor house, or other fortification building of importance. Gatehouses are typically the most heavily armed section of a fortification, to compensate for being structurally the weakest and the most probable attack point by an enemy. There are numerous surviving examples in France, Austria, Germany, England and Japan.
Gatehouses made their first appearance in the early antiquity 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 defence. Strongly fortified gatehouses would normally include a drawbridge, one or more portcullises, machicolations, arrow loops and possibly even murder-holes where stones would be dropped on attackers. In some castles, the gatehouse was so strongly fortified it took on the function of a keep, sometimes referred to as a "gate keep". In the late Middle Ages, some of these arrow loops might have been converted into gun loops (or gun ports).
Urban defences would sometimes incorporate gatehouses such as Monnow Bridge in Monmouth. York has four important gatehouses, known as "Bars", in its city walls including the Micklegate Bar.
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 harmonise with the manor or mansion.
In the Dravidian architecture of South India, very tall gopuram gatehouses, usually four, dominate large Hindu temple complexes.