In this chapter, I discuss passive and mostly ‘low-tech’ defences in the shape of barricades (i.e. counter-intrusion devices) and citadels (i.e. facilities hardened against terrorist or criminal attacks). After all, in my opinion, these modern avatars of time-honoured brick-and-mortar curtain walls still have a formidable role to play in the times of global terrorism: basically, they are our last line of defence against terrorists who have managed to evade all other high-tech measures described above without being detected and are now ready to strike. Hence, I will take a look at modern city walls such as the City of London’s ‘Ring of Steel’/Ring of Glass’, at modern citadels such as One World Trade Center in New York, and at barricades (temporarily) deployed to deny access to certain areas.