Mexico City's main square has a name nobody uses. Officially, it is Plaza de la Constitución, named after the Spanish Constitution of 1812. In practice, everyone calls it the Zócalo, a word meaning "socle," the base of a pedestal.

The name stuck because an independence-era president got no further than laying the plinth for a monument before the money ran out. The pedestal was never built. The square kept the name.

Bare concrete and a flagpole, it is not obviously beautiful. But it sits over the Aztec sacred precinct, flanked by a sinking cathedral built over the Templo Mayor and a National Palace built over Moctezuma's own. Every September 15, the president appears on that balcony, rings a bell, and shouts "¡Viva México!" to a packed crowd below.

VoiceMap's self-guided audio tours use the Zócalo as the starting point for unravelling the layered civilisations beneath it.