The contribution discusses the architectural development of the former (Upper) Ljutomer (Ober Luttenberg) Castle or Lower Castle, which, having disappeared in the nineteenth century, has so far not even been subject to a basic analysis of its architectural history. Although the castle has been long gone and its location, a hill above the village of Podgradje southeast of Ljutomer, is now occupied by a more recent residential building from the nineteenth and twentieth centuries, it still bears great significance for understanding the history of construction in the wider Ljutomer area between the thirteenth and nineteenth centuries. Based on the analyses of preserved old depictions, terrain configuration, and data about the history of the estate as well as by taking into consideration appropriate analogies, it is possible to determine the main development phases of the former castle building with sufficient reliability. Everything suggests that the castle was built in the first half of the thirteenth century as one of many border castles erected by the Archdiocese of Salzburg and that it underwent a dynamic and characteristic architectural development until the eighteenth century.