When enemies attempted to dig tunnels under walls for mining or entry into the city, the defenders used large bellows ( the type the Chinese commonly used in heating up a blast furnace for smelting cast iron ) to pump smoke into the tunnels in order to suffocate the intruders.

When enemies attempted to dig tunnels under walls for mining or entry into the city, the defenders used large bellows ( the type the Chinese commonly used in heating up the blast furnace for smelting cast iron ) to pump smoke into the tunnels in order to suffocate the intruders.

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