Which innovative ingredient did Roman engineers add to their concrete that modern research suggests contributed to its remarkable 2,000-year durability, especially in marine environments?

The ancient Romans were master product designers, creating innovations that have stood the test of time. One of their most remarkable achievements was their concrete formula, which has survived for over 2,000 years - often outlasting modern versions. This poll explores how the Romans approached product design and material innovation in ways that modern product managers could learn from. Test your knowledge about one of history's most enduring product designs!

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Volcanic ash (pozzolanic material)
Fermented goat's milk
Crushed gemstones
Honey and egg whites