i found this passage, maybe someone who knows more about Virgil can tell us about the original context

Decus et Tutamen was suggested by the diarist John Evelyn (1620-1706). It is a line from the Roman poem The Aeneid by Virgil (Book V, line 262), though the poem used it in a very different context. Evelyn had seen it on a printed picture frame in a book belonging to Cardinal Richelieu at the Louvre in about 1644. The idea was simply to stop the clipping of coins, which had become rife with the old hammered coins, though these remained in circulation until the mid-1690s. This passage shows just how potent an issue it could be since it cheated everyone and made the King effectively a cheat too.



One cannot without just Indignation, but deplore the unsufferable Abuse of it, by that cursed Race and Swarms of Clippers, and their Associates in Iniquity …For Money being the common Pledge and Pawn between Man and Man, becomes the standard and Measure of the Worth and Value of everything … he that either diminishes it or sophisticates it, does as much as in him lies, make the King as great a Cheat and Impostor as himself … for which no Punishment seems too great to be inflicted…

That now our current Mill’d Moneys have all this while ben less obnoxious to this injurious practice of Clippers, is certainly due to a less degenerate Age, or the Contrivance of the Circumscription about the Tranche or Edge of the thickest Pieces, and Crenelling of the small and thinner, which for ought I know is Modern and its Inventor (who ever he were) worthy the Honor of Medal himself; whether due to Monsieur Blondeau, our Industrious Rawlins, or Symon (Brother to the late squalid Imbosser) Gravers of the Royal Mint to King Charles the First and Second, or improv’d by the Direction of Mr Slingsby, to whom I suggested the Decus et Tutamen out of a Viniet in Cardinal de Richlieu’s ‘[sic] Greek Testament, printed at the Louvre, hindering his intended addition (in Armis) which neither would have become the Impress, nor stood gracefully in the Circle.

John Evelyn, Numismata, London 1697, 224-5