Director Neil Marshall lived near the ruins of Hadrian's Wall, a Roman fortification built to defend England against Scotland's tribes. The director fantasised about what conditions would cause the Wall to be rebuilt and imagined a lethal virus would work. Marshall had also visualised a mixture of medieval and futuristic elements: "I had this vision of these futuristic soldiers with high-tech weaponry and body armour and helmets—clearly from the future—facing a medieval knight on horseback." The director favoured the English/Scottish border as the location for a rebuilt wall, finding the location more plausible than a lengthy boundary between the United States and Canada. Additionally, Scotland is the home to multiple castles, which fit Marshall's medieval aspect.