Machu Picchu was built without mortar

Inca masons cut stones so precisely that the walls interlock without cement and still survive frequent earthquakes.

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The Eiffel Tower grows in summer

Iron expands when heated, so on hot days the tower can stand up to 15 cm taller — and lean slightly away from the sun.

Venice stands on millions of wooden piles

Its palaces rest on tree trunks driven into the lagoon mud. Starved of oxygen underwater, the wood petrified instead of rotting.

Petra was carved down into the rock, not built up

Nabataean masons started at the cliff top and worked downward, cutting entire facades out of solid rose-red sandstone.

A city carved into a cliff face

Petra was cut directly into rose-red sandstone by the Nabataeans, who also engineered dams and channels that kept a desert city supplied with water.