Churches have often shown potential to be used for defensive purposes. Europe has a substantial legacy of fortified churches which were used for defensive purposes in time of war. There are also example of fortified churches in other parts of the world, for example the Philippines, which was the scene of the Siege of Baler.

Some churches were specially designed to incorporate military features, such as thick walls and narrow, defensive windows. At Ávila the cathedral was incorporated into the city wall. Monastic communities, such as Lérins Abbey, are often surrounded by a wall, and sometimes churches have an outer wall, such as St Arbogast, Muttenz, Switzerland. High concentration of fortified churches can be found in parts of Europe where there was a lot of hand-to-hand warfare, for example in the Dordogne region of France, which was fought over by France and England in medieval times, and in Transylvania, which was the scene of Ottoman invasions.