Thomson derived the phrase Novus ordo seclorum from a poem by the Roman poet Virgil. He wrote that the phrase signified "the beginning of the New American Era" as of the date of the Declaration of Independence in 1776, which was depicted in Roman numerals at the base of the pyramid on the seal.
It is one of two Latin mottos on the reverse side of the Great Seal of the United States

Now is come the last age of the Cumaean prophecy:
the great cycle of ages is born anew.
Now returns the Maid, returns the reign of Saturn:
now from high heaven a new generation comes down.
Yet do thou at that boy's birth, in whom the iron age shall begin to cease,
and the golden to arise over all the world,
holy Lucina, be gracious; now thine own Apollo reigns.