Roman concrete can heal its own cracks.

126

A 2023 study found that lime lumps in the mortar, long dismissed as sloppy mixing, react with seeping water and seal cracks with fresh calcium carbonate crystals.

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The event

• The dome of the Pantheonc. 126 · Rome. The Pantheon, completed under Hadrian, is crowned by a 43-metre concrete dome with an open oculus at the top; its height to the oculus equals its diameter. Almost two thousand years on, it is still the world's largest unreinforced concrete dome.

2nd century

More amazing facts

• 100 Roman public latrines had a sponge on a stick, the tersorium, instead of toilet paper.
• 105 · 751 China had paper by the early 2nd century, but according to tradition it reached the Islamic world only after the Battle of Talas in 751, via Chinese captives.
• 127 The coins of the Kushan king Kanishka show gods from four civilisations: Greek, Iranian, Indian and even the Sumero-Elamite goddess Nana.
• 132 · 138 In 138 Zhang Heng's seismoscope in Luoyang signalled an earthquake that nobody had felt.
• 160 · 1543 For nearly 1,400 years doctors learned human anatomy from descriptions of monkeys.
• 165 · 166 In 166, men claiming to be envoys of the ruler of Rome — probably Marcus Aurelius — reached China.

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