From the time Spanish explorers discovered the Caribbean islands in 1492 until the late 1800s, Spain was a wealthy and powerful nation that dominated trade in much of the western hemisphere, including the early settlements in North America. Because of that influence, Spanish gold and silver coins were often the preferred money for commercial transactions. In fact, Spanish coins were recognized as legal tender in the US until the Coinage Act of 1857.

The basic unit of Spanish currency was the real, and silver eight-real coins were known as Spanish dollars, or colloquially as “pieces of eight.” Those coins eventually became the basis for the US dollar as well as several other world currencies.

Since paper money wasn’t widely used until well into the 19th century, there was a need for higher-denomination coins. Enter the escudo, a Spanish gold coin worth 16 reales. The next higher denomination was a double escudo, worth 32 reales, known in Spanish-speaking lands as a doblón. Its name became anglicized into doubloon. Now you know.

The Spanish doubloon was about the size of a current US half dollar and contained roughly ¼ ounce of 22-carat gold, although they could vary due to fluctuations in the value of gold and the crude manufacturing methods used to produce them. At any given time, the weight was carefully controlled, though, which is one of the reasons it was so popular as a trade currency. Once the coins were crudely hand-stamped, the Spanish mints would weigh them and shave off enough of the precious metal to bring the coin to its proper weight. That’s why the coins tend to be irregular in shape.

While doubloons figure prominently in tales of pirates and treasure, one doubloon actually found its way into US currency—sort of, anyway.

Before the 1789 Constitution, the states were held to be sovereign, and several minted their own coinage. Seeking to land a lucrative copper coin contract for New York, gold and silversmith Ephraim Brasher made a few gold coins modeled after doubloons from the Lima mint in Peru. They never were mass produced; speculation is that Brasher made them to curry favor with New York decision makers. The ploy evidently didn’t work, because Brasher lost his opportunity when the state decided to forgo the making of copper coins.

Only seven Brasher doubloons are known to survive, and the rarest sold for $7.4 million in 2011.