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Figuring Out the Realm for the ‘Coin of the Realm’

If you went shopping in the marketplaces of first century Judea—where the modern nation of Israel now exists—then one of the coins with which you’d buy your groceries would be the prutah. A bronze token of small value, the prutah was minted in massive amounts during a biblically and historically significant period in Judea—from the beginnings of the Hasmonean Dynasty in 134 B.C. until the last years of the Jewish war against Rome around A.D. 69. 

The front and back of a prutah coin
The front and back of a prutah, a coin of first century Judea, scientifically examined by NIST.
Credit: D. Hendin/American Numismatic Society

Among the most common prutot (plural of prutah) were those attributed to either the reign of King Herod Agrippa I (who ruled between A.D. 37 and 44) or his son, Herod Agrippa II (whose kingdom lasted from A.D. 49 to 95). The correct era remained a mystery to historians and numismatists (coin collectors) until 2010 when a team of researchers from the National Institute of Standards and Technology (NIST), Mount Saint Mary’s University, Colorado College and the American Numismatic Society used sensitive nondestructive evaluation (NDE) techniques to determine the elemental makeup of a collection of prutot marked with the name “King Agrippa.” Because ores from a given region typically have unique compositions, this analysis helped determine which mines yielded the copper and lead for the coins.
Combining their scientific data with historical records of when copper and lead mines were operating in Judea and nearby areas during the two kingdoms, the researchers successfully dated the prutot. This is important because the coins are used to help establish timelines for archaeological structures and events leading up to the Great Revolt (A.D. 66 to 73), the first of three major rebellions by the Jews against Roman rule in Judea.

An image of the inside of a Wadi Faynan mine. The blue coloring shows a vein of copper.
A vein of copper within one of the Wadi Faynan mines.
Credit: Milo Inman

The research team performed X-ray fluorescence (to determine their content of arsenic, antimony, copper, lead, silver, tin and zinc) and lead isotope analysis to fingerprint the ores used in the production of the prutot. Traditionally, these NDE methods have not been used on aged coins because corrosion can adversely affect the results. However, the team showed that this obstacle could be overcome using polarizing optics and powerful X-ray analysis software, combined with careful calibration of the mass spectrometer using NIST Standard Reference Materials.

Based on their analysis, the researchers dated the prutot to the reign of Agrippa I. The group also found that the copper for the coins most likely came from the Wadi Faynan region of modern-day Jordan, surprising scholars who thought that specific mine was not reopened until a century later.

Landsape shot of the Wadi Faynan region of modern-day Jordan
The Wadi Faynan region of modern-day Jordan where the copper mines of ancient Judea were located.
Credit: University of Waterloo

Before the 2010 coin analysis, archaeological evidence had suggested that the Romans did not move into the Wadi Faynan area until the second century. The prutot dating suggested that the Romans may have reached the region earlier or found that the Faynan mine had already been reopened. Either way, the findings indicate that the Romans had a much closer relationship with this section of the world than scholars had previously thought.

Did You Know...?

  • Scholars believe that it took 256 prutot to equal one biblical shekel, which is about $20 in modern dollars. Therefore, the prutah would be worth just under 8 cents today.
  • The prutot studied in the 2010 experiment feature a royal canopy (umbrella), the name “King Agrippa” in Greek, three stalks of grain, and a date corresponding to either A.D. 41 or 42. The date is believed to honor the reign of Herod Agrippa I and not represent when the coins were minted.
  • Exposed rocks in the Wadi Faynan region contain bluish copper ore that can easily be removed by hand. Mining in the area began about 4500 B.C., when people discovered that heating the ore yielded a metal strong enough to make tools, religious artifacts, and other objects.

    – Michael E. Newman

    Created June 20, 2017, Updated February 13, 2019