Castles can occur in proximity to one another for various reasons. The periods in which the grounds were used may differ, such that the castles never actually stood near one another contemporaneously. Castles are often directly related when they lie on opposing sides of a “border” or one serves to besiege the other. Chains of castles were needed as blocking systems and as security for border areas. Castles would become proximate to another when dominions were partitioned or expanded. The term “twin castles” can also be used to describe the Ganerbenburg castles that were home to several families at once, in which a “castlein a castle” would create proximity. Compared to proximate castle sites in the Bronze Age, however, those of the Middle Ages were more likely to refer to proximate cities that fulfilled central-site functions, as “megacastles”.