The origins of sterling lie in the reign of King Offa of Mercia (757–796), who introduced the silver penny. It represented the "denarius" of the new currency system of Charlemagne's Frankish Empire. As in the Carolingian system, 240 pence weighed one pound, a unit corresponding to Charlemagne's "livre", with the shilling corresponding to Charlemagne's "solidus" and equal to twelve pence. At the time of the penny's introduction, it weighed 22.5 troy grains of fine silver (32 tower grains; about 1.5 g), so the Mercian pound weighed 5,400 troy grains (the Mercian pound became the basis of the tower pound, which also weighed 5,400 troy grains, equivalent to 7,680 tower grains, about 350g).