BBC:
The tower was discovered in 2015 during the restoration of a building in the Mexican capital.
It is believed to be part of a skull rack from the temple to the Aztec god of the sun, war and human sacrifice.
Known as the Huey Tzompantli, the skull rack stood on the corner of the chapel of Huitzilopochtli, the patron of the Aztec capital Tenochtitlan.
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Archaeologists have identified three construction phases of the tower, which dates back to between 1486 and 1502.