A barbican is a fortified outpost or gateway, such as an outer defense to a city or castle, or any tower situated over a gate or bridge which was used for defensive purposes. Usually barbicans were situated outside the main line of defences and connected to the city walls with a walled road called the neck. In the 15th century, with the improvement in siege tactics and artillery, barbicans lost their significance. However, several barbicans were built even in the 16th century.