For 1,000 years, the walls of Constantinople were unbreakable. Then came a cannon so large it had to be pulled by 60 oxen. Witness the 53-day siege that finally brought the Roman Empire to its knees.

1453 marks the end of the Medieval era. Sultan Mehmed II was obsessed with the Red Apple—Constantinople. To take it, he hired a Hungarian engineer named Orban to build a weapon the world had never seen: The Great Bombard.

This is the story of the last stand of the Byzantine Empire.

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