Roman 22 carat gold "aureii" coin from year 54 AD depicting the head of Emperor Nero

(CNN) -- With the single European currency, as with so many innovations –-shorthand, under-floor heating, the pontoon bridge -– the Romans got there first.

Some 2,000 years before the advent of the euro, the Roman Empire was already practising a form of European monetary union.

It had a single currency, a single system of weights and measures, and -- since all taxes were ultimately set by and delivered to Rome -- a rudimentary form of centralised monetary control.

The Romans first started using coins around 290 BC. As they steadily expanded from their Italian homeland, conquering more and more territory, their coinage -– and language -- went with them.

By the 1st century AD the as, denarius, sestertius and aureus were the common currency throughout Europe, the Mediterranean and the Near East.

There were, of course, regional variations in the buying power of these coins. A litre of beer in ancient Londonium (London), for instance, cost around 16 denarii, almost double what it cost in ancient Barcino (Barcelona).

Lettuces, likewise, were slightly cheaper (by about 1 denarii) in ancient Dacia (Romania) than they were in ancient Gaul (France).

All coinage, however, bore the image and name of the ruling emperor. At a time when it could take up to two months to travel from London to Rome, this symbol of centralised authority was a powerful force for fiscal cohesion.

The Roman Empire was not the only precursor of a single European currency, however.

In the 8th century, for instance, three hundred years after the collapse of the Roman Empire, Charlemagne, King of the Franks, imposed a uniform system of silver coinage on the lands under his control -- roughly equivalent to modern France, Germany, Italy, Belgium, Holland and Luxembourg.

The 9th century Danegeld, a tribute paid by terrified communities across Europe to prevent attacks by marauding Vikings, can likewise be viewed as a rudimentary form of monetary union.

While it didn’t involve a system of economic centralisation in the modern sense of the idea, it did create a financial bond between people from very different lands.

A 9th century Saxon peasant might not have had much in common with an Iberian one, for instance, but both would have been terrified of homicidal bands of axe-wielding Scandinavians, and both would at some point or other have had to cough up to get rid of them.

In more recent times Napoleon (1769-1821) toyed with the idea of a uniform European currency, while the Latin Monetary Union (1865-1926) and the Scandinavian Monetary Union (1873-1924) were both early -- and unsuccessful -- attempts at some form of pan-European economic integration.

It was the Roman Empire, though, that offered the ultimate example of fiscal union, in terms of both its geographical extent -- at its height it reached from Scotland to the Sahara, from Portugal to Iran -- and its centralised authority.

In the early 3rd century, Emperor Caracalla was reputed to have ordered the entire population of Thrace -- roughly modern Bulgaria -- to be sold into slavery for refusing to use standard Roman coinage.

Seen in this light, the euro comes across as both a benign and relatively modest little project.