The most famous story about Archimedes does not appear in any of his books. It was told two centuries later by the Roman architect Vitruvius, in book IX of his treatise On Architecture. Hiero’s crown King Hiero had commissioned a votive crown to offer to the gods and had given the goldsmith an exact quantity of gold. The crown was finished and weighed the same as the gold supplied. But a rumour spread that the goldsmith had kept part of the gold and put the same mass of silver in its place. Hiero asked Archimedes to find out the truth without damaging the crown.