Martello towers spread a compact defensive model across the British Empire

The Royal Navy's difficulty reducing an earlier tower inspired a compact fortification that a small garrison could hold for a long time. Variants carried different numbers of guns and crews, but all sought to concentrate endurance and firepower in a limited footprint. Their distribution from Britain to places such as Sydney makes them a physical map of the early nineteenth-century British Empire. The same model reappeared in World War II pillboxes, which aimed to create small self-contained positions capable of delaying an attacker.