Why build a fortification? A simple question leads to complicated answers that can only be discussed in a wider context. The fortifications of Aigeira are the focus of a project, funded by the FWF that tries to tackle issues around context, chronology, and architecture. Work on the walls started in 2017 and is now a cooperative project of the University of Salzburg and the Austrian Archaeological Institute. The difficulty of dealing with such complicated structures as fortifications, in which political, social, economic and historical issues are inevitably intertwined, motivates to discuss general issues of fortifications in a Greek context, focusing on Hellenistic times, but looking into other periods as well.