The thickness of coins and its evolution

[Luc Andre D]

I started collecting medieval european coins (mostly from France and England but also from Italy and elsewhere) several months ago and I noticed an interesting pattern: most are much thinner than ancient roman or greek coins and also thinner than the coins we use today.
Interestingly also, the few merovingian or saxon coins I have are thicker than later medieval coins from the same countries. Then, if I look at my english and french coins from the seventeenth and eighteenth centuries, they have a thickness similar to that of today's coins.
Elsewhere in the world, some medieval islamic coins were thin (abbassid, omeyyad, ayyubid coins, at least those I have), but not my artuqid and zengid coins, which are rather thick. 
Coins from India, from ancient punchmarks to the moghul dynasty and later, are rather thick. My coins from China are usually thicker than european medieval.
So it looks like there was a period in Europe, from the tenth to the sixteenth centuries, during which coins were made thinner than before or after or than elsewhere in the world. Does anybody know why is that?
(I could not just be wear: even coins not worn out are thin, and besides, roman and greek coins are older than medieval ones.)

[AlexB]

Hi

In the case of Anglo-Saxon I would suggest a lack of materials ie. silver and certainly gold, relative to Roman times and later medieval times. The Romans bought global trade to the table and were an Empire with huge resources. Saxon and later European trade was considerably more fractured and trade became more localised.

Also the Greeks produced fairly substantial coins (as did the Persians), the Romans slightly less so and so on. Maybe the 'token' value of coinage vs its weight/barter value, gained more acceptance over time?

Brgds

Alex

[PeterD]

Early English and continental silver coins were based on the Roman denarius. However, they were less than half the weight of the Roman prototypes but roughly the same diameter. The size would have been more important than weight in establishing a coin's credentials in day to day use, so they had to be made thinner to compensate.

[Luc Andre D]

I think I see something emerging here: after the fall of the roman empire, Europe becomes more politically divided (except when it is briefly unified under Charlemagne) and its trade more fractured; coins become thinner due to lack of resources and remains so until the sixteenth century, which happens to be just after the discovery of the New World (and the birth of new empires like Spain) which brought huge amounts of gold and silver to Europe. Perhaps there was then some devaluation of precious metals, so the coins had to be heavy once again. Nowadays, we use coins which are thicker than medieval ones but made of cheaper metals like nickel, so in the end only the token value survived, gold and silver still being precious metals but not used for everyday currency.
It's fascinating, I really would never have guessed such an evolution had taken place if I had not had the opportunity to handle these coins. Thanks for the input!
(Note: I made a small mistake, actually my saxon coin is also rather thin, so apparently this evolution had already begun in the ninth century or before.)

[AlexB]

Hi

Your point regarding new sources of bullion from America from C15/16thAD onwards is a good one. Later on , throw in Australia, Canada and India.

Brgds

Alex

[khingila]

The conventional wisdom is that the coins of medieval Europe, including the Anglo-Saxon penny, became thin in imitation of the ubiquitous Islamic dirham, itself evolved from the thin drachm of Sasanian Persia.