It is around 150 BCE.
A caravan enters the city just before sunrise.
The gates open onto a crowded market in what is now Punjab.
Camels loaded with cargo disappear into the streets.
Traders unload baskets.
Scribes begin recording transactions, and soldiers weave through the growing crowds.
A man reaches into his purse, pays for his goods, and walks away.
The merchant glances at the silver coins for barely a second before dropping them into a wooden box filled with dozens of others.
Nothing about the exchange seems unusual.
Until we look more closely at one small detail on that very coin, one that would puzzle historians more than 2,000 years later.
