The coin that really blew my mind was a silver denarius minted in 167 BCE in the city of Pergamum, a Hellenistic kingdom that fell under Roman control a few decades later. It’s called the “Attalus II” coin, and it has a double‑headed eagle on the obverse— a rare symbol of dual sovereignty—and on the reverse, a tiny, almost invisible, Roman numeral II, the first known instance of Latin numerals appearing on a coin outside Italy. It was used as a trade token in the Black Sea trade lanes, so merchants in ancient Istanbul and Alexandria could carry a single coin that was recognized by both Greek and Roman authorities. The back story is that Attalus II was a king who wanted to appease Rome without losing his own identity, so he secretly slipped the Latin numeral into the design. When I first saw the coin in a museum, the tiny inscription looked like a joke, but a quick scan with a magnifying glass revealed a faint Roman engraving—proof that coinage was a covert diplomatic language before the age of passports.