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On eBay's Imperial Roman Coin market and History

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EID MAR - An Ancient Roman Coin Commemorates the Assassination of Caesar

eBay's Ancient Roman Coin market is likely the largest market place for ancient coins in today's world.
Hundreds of thousands of ancient items exchanged hands through eBay's marketplace in the last year.

In the last 7 months, more than a quarter of a million coins been listed on eBay alone.

Given the inherit historical value in ancient coins and my personal interest in them, I have been collecting data on every Roman Imperial Coin listing on eBay for the past seven months.

While the data is raw, and the collection continues as I'm writing this article, I found some of the collected data might be of interest to fans of history, data scientists, and collectors alike.

I am yet to draw conclusive points from the study, but have found enough information to personally consider it worth while.

Data science and history don't meet as often as they should, and I hope that with this study I could provide more evidence for the value in the combination.

Data set

The numbers shared here are based on a data-set of 255,568 eBay listings in the Roman Imperial Coins category. Out of which 19.6% sold and the rest died out without a buyer (and most likely re-listed).

The market size

In terms of listings, an average of 194 new listings appear every day, with large spikes on Sundays, as seen in the following chart:

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And in terms of money exchanging hands (i.e, the total sum of the price on sold listings per day) the following chart gives a perspective on the real net market size:

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Note the spike on January 24, caused by a single sell of $75,000.
The coin has since been re-listed.

Coin's Location

Coins exchange hands and resell on international scale, meaning coins originating from Italy or Spain might find their way to other countries and resold there.

As far as exporters of Imperial Roman Coins goes, United States takes the lead by far with 110,313 coins (almost half of the entire market).

But more traditional locations are also sparkling with listings, places like Spain (36,689 coins), and Ukraine (11,477 coins) are more in line with the traditional Imperial borders, as can be seen on the map:

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Disregarding the new world

It is clear that Imperial Roman Coins didn't end up in North America by Roman expansionism and rather by modern trade, and as such offer little historical value.

Disregarding locations that were unknown to the Romans gives us a map more similar to what one might expect:

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Trajan on the map

Global all inclusive data might hide some delicate and interesting details.

When mapping up all the listing that were listed as minted under Trajan, a complete different image is shown, one where modern day Ukraine is the main exporter by a large margin:

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This is interesting, as Trajan is known for conquering the area known as Dacia, which is around modern day Ukraine. The correlation might be coincidental, but the symmetry is definitely interesting.

Trajan Rome Map

This in comparison to the mapped listings of Augustus minted coins:

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Possible indicators for inflation and economical issues

When attempting to find out the most common face on imperial coins I found that I could could gather much more than that.

Assuming the listing are some-how representative of all minted Roman coins (which clearly is not the case, but is just about enough to draw first and rough conclusions), one can find out how many coins of a specific ruler were minted per year of his rule.

With this information, one could see quite simplistic yet interesting indicators for the economical state and inflation during different periods of the empire.

When the economical situation in Rome was in shambles, it often lead to extreme cases of inflation and debasement.
While the data-set is not sufficient to determine debasement of coins, it is large enough to find out how many coins a ruler minted per yer of his rule:

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As the chart above shows, Constantine II takes the crown, with 994 coins per year of rule, which indeed correlates with historical data we have about the inflation during his rule:

...in Diocletian's time, in the year 301, he fixed the price at 50,000 denarii for one pound of gold. Ten years later it had risen to 120,000. In 324, 23 years after it was 50,000, it was now 300,000. In 337, the year of Constantine's death, a pound of gold brought 20,000,000 denarii.

"The year of Constantine's death" would also be the year before Constantine II's starting rule. In that sense, it seems that Constantine II's ruler could have been affected by the changes in Constantine I ruler more than Constantine the Great himself.

Further work and collaboration

The chars and indicators above would be obviously interesting for the crowds to which this article is intended, but no strong significant historical conclusions were drawn out of it yet.

For the foreseeable future, I will continue to collect data and attempt to analyse it for more interesting data.

As a full time employee, I can not dedicate enough hours to this project as I wish. If you wish to collaborate on this project, have good insights, or/and a strong background in statistics / Roman History, please email me at dzautner@gmail.com and we could discuss the project and it's future direction.