Lord of the Rings fans will recall the beacon fires of Gondor, where flames were lit in successive towers along a mountain range to signal war. The Svan defense towers served much the same function. When the Svan came under attack, which they frequently did, beacon fires would spread across the towers signaling a call to arms. The towers also doubled as fortified shelters that non-combatants could barricade themselves within and in some cases would live in as their regular home.