As promised, a contribution to the thread with an actual coin, not just blabbering. 
Louis I, Francia/Frankish Kingdom, denier, 822-40. Inscription: HLVDOVVICVS IMP / XPISTIANA RELIGIO.

Louis I, son of Charlemagne, succeeded his father in 814 and ruled the Frankish kingdom until his death 840. Due to his piety he usually goes by the name Louis the Pious.
The historical significance here is twofold:
Firstly, Louis was the last of the Carolingian kings to rule the whole of the vast Frankish kingdom, stretching from Rome and the Mediterranean to the North Sea, and from the Atlantic to what is today Austria. He decided that after his death, the kingdom should be split among his three sons, in a western, a middle, and an eastern part. Following his death in 840, his sons immediately began fighting over the parts (Louis had not divided the kingdom equally, his favorite son Lothair would have the larger, middle, part). After enough fighting they came to an agreement and in the treaty of Verdun 843, the three new kingdoms West Francia, Middle Francia, and East Francia were established. West Francia eventually became France; Middle Francia became Lorraine, the Low Countries and northern Italy; East Francia became the larger part of the Holy Roman Empire and later Germany. Lorraine became a fighting ground for armies from the neighboring West and East kingdoms/nations over the centuries, latest and hopefully for the last time, during WW2. Had the pious Louis known that he was laying the foundation for a thousand years of battles, he might have acted differently.
Secondly, this is an early example of a coin minted according to Charlemagne's monetary reform of (around) 780. It stated that one livre (pound, as a weight measure) was divided into 20 sous, each in turn divided into 12 deniers (each containing 1/240 of a pound of silver). This division lasted for over a thousand years until the decimalization of French money in 1793. As is well known, the system spread to other countries as well. In Britain, the 1 pound = 20 shillings = 240 pence division lasted until 1971 (still using d to denote the penny, originating from denier; the £ sign for pound comes, of course, from the word livre).

Louis I, Francia/Frankish Kingdom, denier, 822-40. Inscription: HLVDOVVICVS IMP / XPISTIANA RELIGIO.

Louis I, son of Charlemagne, succeeded his father in 814 and ruled the Frankish kingdom until his death 840. Due to his piety he usually goes by the name Louis the Pious.
The historical significance here is twofold:
Firstly, Louis was the last of the Carolingian kings to rule the whole of the vast Frankish kingdom, stretching from Rome and the Mediterranean to the North Sea, and from the Atlantic to what is today Austria. He decided that after his death, the kingdom should be split among his three sons, in a western, a middle, and an eastern part. Following his death in 840, his sons immediately began fighting over the parts (Louis had not divided the kingdom equally, his favorite son Lothair would have the larger, middle, part). After enough fighting they came to an agreement and in the treaty of Verdun 843, the three new kingdoms West Francia, Middle Francia, and East Francia were established. West Francia eventually became France; Middle Francia became Lorraine, the Low Countries and northern Italy; East Francia became the larger part of the Holy Roman Empire and later Germany. Lorraine became a fighting ground for armies from the neighboring West and East kingdoms/nations over the centuries, latest and hopefully for the last time, during WW2. Had the pious Louis known that he was laying the foundation for a thousand years of battles, he might have acted differently.
Secondly, this is an early example of a coin minted according to Charlemagne's monetary reform of (around) 780. It stated that one livre (pound, as a weight measure) was divided into 20 sous, each in turn divided into 12 deniers (each containing 1/240 of a pound of silver). This division lasted for over a thousand years until the decimalization of French money in 1793. As is well known, the system spread to other countries as well. In Britain, the 1 pound = 20 shillings = 240 pence division lasted until 1971 (still using d to denote the penny, originating from denier; the £ sign for pound comes, of course, from the word livre).