The system bestowed upon the West by Charlemagne and his son Louis the Pious was both long-lasting and coherent. The idea of minting pure gold had become a utopian dream, bimetallism an impossible luxury. The gold coin of the Roman Empire—its very name, solidus, indicating a reliability unaffected by time or place—was nothing but a memory in the minds of a few learned clerics. Even the triens, a third of a solidus, was becoming increasingly rare; they were hoarded, melted, or exported.
Charles minted a few coins for form's sake, asserting the claim of the Frankish kings to be heir to the Caesars with some triens issued in northern Italy and Tuscany. It was more a matter of exercising his sovereign right to mint in gold than of enhancing economic life by furnishing it with a means of exchange based on something other than the old practice of barter.
The West did not have enough gold to allow itself such a coinage, and the gold that was minted rapidly disappeared from use as money. The emperor Louis the Pious was to be the last, around 820, to mint a triens, which was apparently never seen in circulation. The only gold coins encountered were the odd Byzantine hyperper or the occasional Arab coins from Spain or Sicily—otherwise nothing.
So it was not with gold that payments were made, but with good silver deniers. Louis the Pious had laid down strict instructions in about 825 that 240 of these coins should be struck for one pound in weight (equal to some 490 modern grams) of silver. Thus a denier weighed approximately two grams.
The first devaluation, in 865, was the work of Charles the Bald. The denier became lighter, and for a pound of silver 264 coins were minted.