Sixteenth-century writers described a huei tzompantli, a great rack of skulls, standing in the ceremonial precinct of Tenochtitlan, the crania threaded on horizontal poles through holes cut at the temples. For four centuries this was known only from those descriptions, and descriptions of that kind, written by men who had come to conquer the place, are exactly what a careful reader discounts.
From 2015 the Programa de Arqueologia Urbana, working on Calle Guatemala a short distance from the Templo Mayor, found it. The excavation exposed rows of skulls pierced at both temples, consistent with the described rack, and beside them a circular structure in which skulls had been set into mortar to build a tower. The skulls in the tower face inward, which means they were mortared as construction material rather than displayed, and that had not been described by anybody.
Two things follow immediately. The tzompantli was a real structure of the kind reported, which is a point for the descriptive content of the colonial accounts. And the assemblage is not what the accounts imply it was. The dominant colonial picture is of captured enemy warriors; the excavated skulls include women and children in numbers that no reading of that picture accommodates. The structure records something wider than the disposal of prisoners of war, and what exactly is a question the excavators have not closed.