From the time of Charlemagne until the French Revolution, currency was fluid in value but
consistent in names used. Two names appear most frequently: livres and francs. These came in
and out of use, and even existed concurrently with one another and with the ecu. They changed
in the standards on which they were based (gold or silver), in the values or weights by which
they were measured, and in their base of counting (dozen, then twenty, and finally a decimal
system in later centuries). Originally one livre was equal to one pound of silver. There were two
main different types of livres: the Parisis and the Tournois. Minted in multiple places, the livre
that was most consistent and of the highest quality in craftsmanship was the one made in Tours,
France, which became known as the livre tournois. The livre was generally the standard used
for accounting in all contracts in France but was abolished briefly from 1577 to 1602 when the
standard unit became a gold coin, the ecu.
The franc originated as ransom raised to free King Jean II from the English in 1360 A.D during
the Hundred Years War. The franc was the first coin minted that was worth one livre tournois.
Originally gold, it became silver from 1577 until 1641. The silver ecu, the franc, and livre
tournois all existed after 1641 and were used interchangeably. These were subdivided into 20
sous or sois for one franc or 240 denier tournois, hence 1 sous equalled 12 deniers tournois.
The monetary system based on a dozen existed up to the French Republic when in 1795 it was
switched to a decimal system with one franc equal to 10 decimes or 100 centimes. The Franc
was again revived in 1803 by the Empire as a gold coin with Napoleon on it, giving it the
nickname d’or Napoleon or gold Napoleon. With Napoleon’s fall in 1815, the system returned to
the decimal franc previously adopted by the Government of the Revolution.
For tables of various values for French currency over time and locality, see Memoire sur les
variations de la livre tournois depuis le regne de Saint-Louis by Natalis de Wailly (Paris:
Imprimerie Imperiale,1856.).
For further information:
About the franc, consult: Wikipedia French and Wikipedia Fench Franc
About the livre tournois, consult: Wikipedia Livre Tournois 
About the ecu, consult: Wikipedia Ecu
For assistance in converting values in French historical currencies found in documents, see: Historical Statistics Currency Converter

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