"Neither snow nor rain nor heat nor gloom of night stays these couriers from the swift completion of their appointed rounds." While the Postal Service has no official motto, the popular belief that it does is a tribute to America's postal workers. The words above, thought to be the motto, are chiseled in gray granite over the entrance to the New York City Post Office on 8th Avenue and come from Book 8, Paragraph 98, of The Persian Wars by Herodotus.

Source: United States Postal Service