‘Romanesque’ elements, such as voluntarily rough-looking pillars and vaulting, were used in the architecture of the early modern nobility in the Southern Low Countries to suggest ancientness. This working hypothesis needs to be tested more widely across the different lands of the Habsburg federation, when a more thorough archaeological examination, not hampered by set views on the evolution of the castle, will be available for a greater number of cases. One particular component of twelfth-century architecture, the keep, shows up again in the architecture of the duchy of Brabant during the fifteenth century and serves as a source of inspiration for a new type of hunting pavilion in the seventeenth century. The square tower with square corner turrets is pioneered by Charles III of Croÿ, duke of Aarschot, in his renovation campaigns at Rotselaar en Bierbeek (1601–1604), and subsequently serves as model for the extension of Mary of Hungary’s Mariemont under Albrecht of Habsburg and Isabella of Spain (1618–1621). It then becomes popular with the Netherlandish nobility elevated to baronial rank by Philip IV.