Uncovering the Aztec tower of skulls
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Uncovering the Aztec tower of skulls in Mexico City

More than 650 skulls once used to terrify the Aztec's enemies have been discovered in Mexico City.

The skulls formed part of the skull rack known as the Huey Tzompantli, which sat next one of their most important temples in 1521.

One of the returning Spanish conquistadors described how the Aztec capital was filled with tens of thousands of skulls - a terrifying prospect for the invading soldiers.

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