Tsar Pushka is a huge cannon that is located inside the walls of Moscow Kremlin. It weighs nearly 38 metric tonnes and has a length of 5.34 meters. It is believed that the Tsar Cannon has never been used. It may in fact have been intended as a showpiece of military might and engineering from the beginning. The cannon is decorated with reliefs, including one depicting Tsar Feodor Ivanovich on a horse. The cannonballs on display by the Tsar Cannon were never intended for use, and are in fact of a larger diameter than the cannon can accept.

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Adapted from Wikipedia - Tsar Cannon