Nowadays, the North-Eastern Netherlands is not known for being a region with many castles. But in the Middle Ages, at least 134 episcopal castles, noble houses and fortifications existed here. This area, known as the Oversticht, was part of the episcopal principality of Utrecht in the Middle Ages. In this thesis, the development of the Oversticht castles is analysed in relation to space and time between 1050 and 1450. To this end, a new methodological and theoretical approach is introduced: the castle landscape model. This model offers the opportunity to research the interaction between castles and their environments in an interdisciplinary and diachronic manner. This is done at various scales: first, the territorial castle landscape of the Oversticht is mapped, in which castle development and the interaction between the physical landscape and construction of territorial power of the prince-bishop of Utrecht are central. Consequently, the interaction between castles and their environments is studied in more detail through two partial studies. The first partial study concerns the oldest castle site: the mysterious castle of Hunenborg (Volthe, Twente), which is surrounded by a circular rampart and located in the wilderness. The second partial study focuses on the micro-region of South-west Twente and describes how the lords of the castles of Goor and Diepenheim left a significant mark on the landscape. Finally, the results are compared with the areas of Nedersticht Utrecht and Sticht Munster and evaluated in relation to national and international discussions in research on castles.