“Neither snow nor rain nor heat nor gloom of night stays these couriers from the swift completion of their appointed rounds.” If this motto summons up visions of brave postal workers trudging through inclement weather conditions, you’re not alone—for over a century, it’s been synonymous with the tireless work the postal service does to make sure you get your junk mail, magazines, and birthday cards on time. But if you think it’s the official creed of the United States Postal Service, think again—it was actually written about another set of postal workers from around 500 BCE.

In fact, the USPS doesn’t have an official motto [PDF]. And given that the postal service regularly cancels mail delivery due to weather, the misunderstanding about its motto regularly leads to even more frustration from mail-less customers.

Blame a building for the confusion. In 1912, a building then called the General Post Office Building (since renamed the James A. Farley Post Office Building) was constructed in what would later become ZIP code 10001. Smack in the center of Manhattan, the grand building was built right across from Penn Station and Madison Square Garden. It had prime real estate and a profile to match—white columns, a grandiose reception hall, and even a dry moat around it to light up its gigantic basement.

It also had an architect with a taste for classical flair. William Mitchell Kendall designed other column-studded sites like the Manhattan Municipal Building and the Arlington Memorial Bridge. Kendall, whose dad was a classics scholar, also loved the words of the ancients as much as their columns. So when he designed the post office, he decided to inscribe it with a phrase by Herodotus, the Greek scholar sometimes known as the father of history.

Kendall modified a translation of Herodotus’s work by George Herbert Palmer, a professor at Harvard and a preeminent classicist, for the building. The line was written by Herodotus in paragraph 98, book eight of his book The Persian Wars, which recounts the history of a war that took place between the Greeks and the Persian Empire from 499 to 479 BCE (the exact time period of the war is disputed).

Herodotus was impressed by the efficient, relay-like postal system employed by the Persians, which he compared to the Greek torch race. “There is nothing in the world which travels faster than the Persian couriers,” he wrote admiringly. The postal system may have been impressive, but it ultimately didn’t help Persia—after decades of conflicts, they lost the wars.

The Persians may not have won in Greece, but the Persian couriers who inspired the inscription must have been on to something—to this day, the USPS relies on a relay-like system to both get mail across the country and help postal carriers on their daily rounds. They may not operate in all weather conditions, but today’s USPS still manages to deliver hundreds of billions of pieces of mail each year. Not bad for an organization with no official motto.