Alexander of Macedon was just twenty years old in 334BC when he set out with a small army to challenge Persia, the largest and most powerful empire in the world. The Macedonians marched East into the unknown, won battles against overwhelming odds, stormed impregnable fortresses. In the deserts and mountains between the Aegean and India they conquered nature itself. Yet disaster was never more than a sword stroke away. Alexander’s companions were riven with murderous rivalries, their loyalty contingent. The threat of treason, inspired by ambition and Persian gold, or by honour and principle, was ever present.