Teohuacan's mica layers — what kind of 'religious use' requires industrial radiation shielding

This drove me insane when I first read about it. Teotihuacan near Mexico City — massive pre-Aztec city, the Pyramid of the Sun and all that — was excavated extensively through the 20th century. In the 1900s, workers found a thick layer of mica sheets sandwiched between two of the pyramid's courses. ……