Gatehouses have existed since antiquity – as early as there have been fortifications to protect. Initially smaller and simpler, gatehouses evolved over time into much more complex structures containing multiple lines of defence.
Fortified gatehouses usually included a drawbridge, one or more portcullises, arrow loops, and murder holes from which to throw hot liquids, stones, and missiles on attackers. When they were heavily fortified, they could also take the function of a keep.
Some casles had more than one gatehouse. For example, has four of them (called Bars) in its city gates.
At the end of the Middle Ages, most gatehouses were converted into decorated grand entrances designed to hamonise with the manor or mansion. Many of them became separate free-standing buildings.