<p>While fortification walls primarily aimed to protect against invaders and demarcate city boundaries, their construction posed significant challenges for Greek architects and engineers. These walls obstructed water management routes that relied on topography and gravity for flow, such as long-distance Greek aqueducts. These long-distance water sources sustained larger settlements when nearby sources, such as wells and cisterns, were insufficient to meet water demand. While this prevented fresh water from coming in, it also prevented the expulsion of waste and rainwater that collected along the walls, especially in cities built on slopes. To address these issues, Greek architects and engineers devised a system of underground passages, isolated sewers, and breaches in city walls, which created both defensive and structural vulnerabilities. This article highlights the architectural features of northern Greece during the Archaic, Classical, and Hellenistic periods, showcasing distinctive hydraulic elements found exclusively in the region’s fortifications.</p>