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.