Urban conversion of bastion-type fortifications

Conversion of bastion-type fortifications in European towns in the second half of the 19th and early 20th century resulted in some of the most significant and most valuable examples of urban interventions of the period. In 19th and 20th centuries, when these fortifications underwent conversion, new city areas were created which today constitute the very nucleus of their respective towns.

Intensive demolition, which began around mid-19th century, opened up new possibilities not only in terms of physically linking formerly separated parts of the city, but also in terms of freeing up valuable stretches of land in city centers which were, as a rule, reserved for creating representative city areas. As the threat of Ottoman conquests diminished and the defense line of the Habsburg Monarchy moved eastwards, as well as owing to the change in warfare due to modernization in fire arms, bastion-type fortifications in Northern Croatian towns gradually lost their intended purpose, the need for their upkeep ceased over time, they became a major obstacle to urban development and by the early 19th century there was strong initiative for their demolition and integration into the urban fabric.

Due to urban importance of areas created on the site of former bastion-type fortifications, analysis of conversion processes in seven Northern Croatian towns (Bjelovar, Karlovac, Koprivnica, Kriievci, Petrinja, Osijek and Varaidin) was made. The analysis was carried out by the previously established research method in order to gather the same type of data concerning building features and conversion processes for all cities as a basis for a comparative analysis with the aim to define their similarities and differences and identify certain regularities in conversion processes.

The second part of the research focused on developing the method for researching urban features of areas of former fortifications at the beginning of the 21st century. The method was then applied on several Croatian and European cities, thus making possible their mathematical and statistical commensurability and defining characteristic types of such city areas. The aforementioned research method was based on proposing one single model of analysis which, when applied on each chosen city, gathers the same type of data (by breaking down the city into important urban elements) and the collected data are then analyzed in seven analytical groups.

The results obtained through analyses of areas created by the conversion of former fortifications in European cities lead to the conclusion that the majority of urban interventions undertaken in the late 19th and early 20th centuries do have certain shared features, namely that these areas, created by the city spreading inwards, have indeed become areas of dense concentration of public buildings. Their shared urban features stem primarily from similar traffic system organization and use and less from shared building features of insulas created on the site of former fortifications. The research has identified the types of areas created with the conversion of bastion-type of fortifications as well as their urban features; these areas have established new identity and created new urban values and can serve as a basis for defining guidelines for future urban planning in (Croatian) towns. Furthermore, a comparison of Croatian and European towns belonging to the same integral type according to urban features of their areas of former fortifications, together with a comparison of all defining elements of the urban situation in each exemplary case (building structure, purpose of insulas, traffic system) can be used as an additional criteria and one of the starting points for contemporary interventions in the case of Northern Croatian cities which are spreading inward, primarily when the spreading means conversion of former bastion-type fortifications.

Defense towers of the Castles

Defense towers were an important element of the castles built between the 13th and 15th c. They were intended not only for defense but also for accommodation and were strategically placed where attacks were expected, more rarely at the entrance to the castle. In the course of time they were modified, modernized, and better fitted for accommodation or defense purposes. In most cases they had square or rectangular plans up to 12/12 m although some plans were different in shape. With the invention of fire-arms they lost their original function.


The nucleus of the castle was a defense-tower, a tall tower with strong walls for defense and safety purposes. The defense tower dealt with in this paper were built from the 13th century until the end of the 15th century. In the early 16th century a new type of defense tower used to be built in Croatia. Circular in plan, built for defense purposes against the Turks, it already formed a part of Renaissance castles.

In the Middle Ages, defense of the castle was organized from top of the walls between the merlons of the battlements whereas the purpose of the defense tower, due to its height, was the successful control of the territory and defense under siege. The aggressor used to build tall mobile wooden towers which were slowly drawn towards the castle in order to demolish the walls with a battering ram and break through to the top of the walls. This element of the medieval siege strategy was the primary reason for raising the defense towers to such heights. They had to be at least as tall as the aggressor’s wooden siege tower or even taller. The top of the defense tower was fitted for actions against the aggressor. Defense towers in continental Croatia (13th-15th c.) fall, according to their purposes, into three groups: defense towers for defense purposes, defense towers for both defense and accommodation purposes, and multi-purpose defense towers intended for defense, entrance to the castle and accommodation. A special type of structure was an “accommodation tower” which is reminiscent of the defense tower in terms of its volume and some organization features. However, it was more a palace-type structure which deserves to be analyzed separately.

The first towers were intended for defense relying on their height as the most important element since their role was the control of the territory. For this reason they had to be taller than the aggressor’s siege-type tower. The most important was the top storey. These defense towers were mostly smaller square-shaped structures oriented by their angle to the expected attack.

The second type of defense towers intended for safe accommodation in addition to their defense purpose soon followed. It was a more elaborate type of tower, bigger in size integrating the two functions: defense and safe accommodation. However, this type of organization does not exclude the construction of a palace nearby. They were accessed from the first floor, usually over a drawbridge or a ladder which, when lifted up, ensured safety overnight as well as during siege. The top of the defense tower was used for defense under siege.

Several examples of multi-purpose defense towers have been preserved. They originated in different historical periods and therefore exhibit considerably distinct features.

Owing to the fact that most towers were demolished or left as archaeological traces, the research work usually concentrates on their plans as these are generally the most easily available. The plan of the “true” defense towers was most commonly square and rectangular whereas the accommodation ones were triangular, polygonal or circular. There was even an example of an octagonal plan. In case of square, triangular and polygonal plans, a typical feature was the orientation of the angular parts towards the direction of enemy attack. Defense towers were normally placed on one end of the castle above a diagonal ditch. The slanting wall was more difficult to break through with a battering ram, also it was more difficult to lower a drawbridge from the top of the wooden siege tower.

Schematic drawings of sections made by some authors show the same features that are also more or less found in our regions: the defense tower comprised the ground-floor, one to three (four) storeys and a defense-purpose loft. There was no basement since the castles were mostly built on rocky terrain. In the accommodation defense towers, the second floor was obviously intended for housing.

The interior arrangement was conceived during the construction stage. It is evident in various elements such as stone benches in window niches, fireplaces, cantilevered toilets, small niches for candles etc. Possible partition walls were made of wood although the defense tower in Poeitelj featured partition walls made of stone.

The defense function of the towers is confirmed by their positions along the ditches and their general relationship to the ground plane outside the castle walls. The height of the defense tower had to match the height of the siege tower. Some defense towers differ as far as their construction is concerned. Each of them was a unique structure, yet they shared a myriad of common features. It seems that the use of siege wooden towers diminished over time due to the invention of fire-arms as well as the new strategies of attack and defense. The fact that the defense towers were no longer an integral part of the north Croatian castles by the mid 15th century, when many of them were partitioned or remodelled by additions, is rather significant (Cesargrad, Kostel, Lobor, Kamengrad near Pozega, Ruzica). The same happened to the first castles in Slavonia. Defense towers reappeared in the period of Turkish invasion; however, their concept was different.

The comparative analysis of those defense towers that can still be researched indicates that there is a correspondence between them and the type of defense towers in central European countries. Architecturally, however, Croatian defense towers from the period between the 13th and 15th centuries were more modest than the central and west European ones. Many castles with their defense towers were demolished in the wars against the Turks during the 16th and 17th centuries. Some of them were demolished intentionally whereas others were partitioned or simply left to decay. Even later no particular effort was ever made to preserve them so that today we are left with nothing more but the “remains of the remains”.