Pearl

In the year 38 BC, Cleopatra wagered Marc Antony she could give the most expensive dinner in history.

Cleopatra aimed convince the Roman ruler that Egypt possessed enough wealth to put it above conquest. As Anthony reclined the Queen removed an earring, crushed a single large pearl, dissolved it in wine (or perhaps vinegar), and drank it. Astonished, Antony declined his dinner — the matching pearl — and admitted she had won.

100 years later Pliny the elder, in his famous manuscript Naturalis Historia, estimated the value of a single pearl to be 29 TONS of fine silver (or about $30 million dollars). Such was the rarity of the pearl in ancient times.