Fortress church

A fortress church () is a particular type of church that, in addition to its religious functions is also used by the local population as a retreat and defensive position, similar to a refuge castle. A fortress church usually implies that the church is enclosed by its own fortifications, such as curtain walls and defensive towers. By comparison, a church with simple defensive features, such as battlements and embrasures on the church itself, is usually just referred to as a fortified church.
Architectural history.
The fortress church is typically surrounded by defensive walls equipped with wall towers and wall walks. It is a development of the fortified churches, whose defensive walls were also the actual walls of the church. Although the terms are often used interchangeably without clear distinction, a fortified church properly refers to a single building whereas a fortress church is a building complex. Construction of defensible churches evolved over time. Earlier constructions included a church surrounded by barns in which a siege of several days could be endured. Then fortified cemeteries ("Wehrfriedhof") arose and simple fortified churches, to finally the fortress church. The fortress churches surviving today date from the 15th century. 
Unlike the populations of towns and cities, villagers could not afford to build defences around an entire settlement. The fortress churches were often the only stone building in such places and so were the population's only refuge from the violence of the military conflicts, the local raiding and plundering that often accompanied military campaigns, as well as providing defence against nomadic bands of marauders. 
In the Early Middle Ages, especially in recently Christianised regions like Saxony, former bishop's seats were designed as fortress churches. In Saxony they were referred to as a "Domburg" or "cathedral castle". Fortress churches are especially common in Franconia, South France and Transylvania (Romania). Particularly in Transylvania, a historically German settlement area, there are well over a hundred fortress churches of which seven have been designated as UNESCO World Heritage Sites (Birthälm/Biertan in 1993, Kelling/Calnic, Wurmloch/Valea Viilor, Dersch/Darjiu, Deutsch-Weißkirch/Viscri, Keisd/Saschiz and Tartlau/Prejmer in 1999). These were established in order to defend against successive Turkish invasions.
Fortress churches have not survived in North Germany, most likely due to the re-use of their stone for other building purposes during period of scarcity of such materials. The only well-known fortress church in the coastal region of North Germany is the Church of St. Dionysius in Bremerhaven-Wulsdorf, which is recorded as having a field stone curtain wall up to 3.60 metres high.
List of places with surviving fortress churches.
Germany.
Bavaria.
County of Kulmbach
County of Eichstätt:
County of Bad Kissingen:
Landkreis Cham
County of Erlangen-Höchstadt
County of Forchheim:
County of Haßberge:
County of Kitzingen:
County of Main-Spessart:
County of Miltenberg:
County of Neustadt/Aisch – Bad Windsheim:
County of Rhön-Grabfeld:
County of Schweinfurt:
County of Würzburg:
County of Passau:
City of Nuremberg:
Lower Saxony.
County of Osnabrück:
Thuringia.
County of Hildburghausen:
County of Schmalkalden Meiningen:
Saxony.
County of Görlitz
Romania (Transylvania).
Among the dozens of well-preserved fortified churches in Transylvania (present day Romania), seven of them are located in the UNESCO World Heritage Site inscribed in 1993 as the villages with fortified churches in Transylvania.