The Metropolitan Cathedral of Mexico City was built on a problem.

The Spanish, determined to construct the largest cathedral in the Americas over the ruins of the Aztec Templo Mayor, soon discovered that marble was far too heavy for the waterlogged soil beneath the Zócalo. They switched to volcanic rock, porous and light.

Even so, by the 1960s, after 250 years of uneven sinking, UNESCO listed it among the world's ten most endangered structures. That slow subsidence is just the beginning. The cathedral took two centuries to finish, which is why its facade is a running argument in stone: Doric columns at ground level, Ionic above the entrance, and Solomonic Baroque columns flanking the side doors.

VoiceMap's self-guided audio tours trace how the cathedral's volcanic tuff and the Sagrario's ornate Churrigueresque stonework arose from the layered history beneath the Zócalo, connecting Aztec foundations to colonial ambition.