Not so long ago, the systems that power our physical world, such as factories, water treatment plants, and energy grids, ran in relative isolation. These are examples of Operational Technology (OT) environments, systems that control industrial equipment and processes. Protected by the reassuring concept of the air gap, they operated with no internet connection and, seemingly, little risk. Fast forward to today, and that separation has all but disappeared. OT environments are now connected, increasingly exposed, and becoming more frequent targets—yet many organisations still struggle to secure them effectively. In this talk, we’ll explore how OT security has evolved, from the early days of relying on physical separation, to today’s complex landscape of cyber-physical threats, ransomware, and blurred lines between IT and OT. Using the metaphor of an ancient wall, we’ll consider why modern OT security requires more than just a strong perimeter. It calls for layered defences, thoughtful design, and, crucially, skilled people who understand how to apply the tools at their disposal. We’ll also look at the cultural divide between OT engineers and cybersecurity professionals, highlight the value each side brings, and suggest ways to foster better collaboration. Whether you’re responsible for securing critical infrastructure, working with industrial systems, just curious about OT, or simply intrigued by how these environments are evolving, there should be something in this talk for you.