A single boundary might, upon closer inspection, reveal eons of history—from epic tales of conquest, treaties, and alliances to intimate, all-too-human stories of love, greed, and folly. None of the lines we know today were inevitable, and all might have looked quite different if not for the intricate interplay of chance and ambition. From the very first maps in Egypt to the Roman attempts to define the boundaries of civilization, from the profound shift in meaning of the Mason-Dixon Line to the secret British-French agreement to carve up the Ottoman Empire during the First World War, and from the dark consequences of Detroit’s city limits to the intriguing reason why landlocked Bolivia still maintains a navy, this is a singular look at all of human history—told through its most captivating border stories.