The denier was a medieval coin which takes its name from the Frankish coin first issued (as the denarius) in the late seventh century; in English it is sometimes referred to as a silver penny. Its appearance represents the end of gold coinage, which, at the start of Frankish rule, had either been Byzantine or "pseudo-imperial" (minted by the Franks in imitation of Byzantine coinage). Silver would be the basis for Frankish coinage going forward.
In the eighth century, Charlemagne introduced an accounting system in which 12 deniers equaled one sou and 20 sous equaled one livre. Also three deniers equaled one liard. Only the denier was an actual coin; the others were "money of account", used only for accounting. This system and the denier itself served as the model for many of Europe's currencies, including the British pound, Italian lira, Spanish peseta and the Portuguese dinheiro.