London Rainstorm Reveals Trove of 300 Iron Age Coins

The “once-in-a-lifetime find” includes 2,000-year-old potins featuring stylized images representing Apollo and a charging bull

Pile of potins
Known as potins, the 2,000-year-old coins were crafted out of a copper, tin and lead alloy. HS2

A rainstorm in London has led to the discovery of a hoard of more than 300 coins dated to the first century B.C.

Archaeologists were nearing the end of an excavation in Hillingdon, along the route of the HS2 railway project, when rain changed the ground conditions, BBC News reports.

“[W]e found a patch of soil that was a very different color from what it would be expected to be,” says Emma Tetlow, historic environment lead for the Skanska Costain STRABAG joint venture, which is leading the HS2 digs, in a statement. “The patch of soil was dark greeny-blue which suggests oxidized metal, and when we checked more closely, we could see loosely packed metal discs.”

The Iron Age coins—known as potins due to the copper, tin and lead alloy used to make them—each measure about 1.2 inches in diameter. They show stylized images representing the Greek god Apollo on one side and a charging bull on the other.

As Aaron Morby reports for the Construction Enquirer, the potins’ design was based on coins made in Marseille, France, about 2,175 years ago. Over time, these early coins spread across northern Europe.

In England, potins have mostly been found around Kent, Essex and Hertfordshire. People in Britain may have begun making the coins around 150 B.C. The earliest versions were bulky disks known as Kentish Primary, or Thurrock, types. Comparatively, the newly discovered potins—now dubbed the Hillingdon Hoard—are of the “flat linear” type, which uses simplified and abstracted images. Researchers have found similar coins from the late Iron Age, but in much smaller quantities.

The hoard’s purpose is unclear, as coins were generally not used as currency in first-century B.C. Britain. (Instead, notes the statement, bartering was the main method of exchange.) The potins may have represented an offering to the gods or a method of marking a boundary. Hoards also sometimes acted as emergency savings.

According to the researchers, the find dates to around the time that Julius Caesar’s Roman forces first invaded Britain, in 55 and 54 B.C. Per English Heritage, the Romans did not conquer the region at that time, instead reaching a peace with its leaders. The Roman Empire maintained a diplomatic relationship with Britain for about a century, until 43 A.D., when Emperor Claudius mounted an invasion that eventually led to the empire’s expansion into the region.

London Rainstorm Reveals Trove of 300 Iron Age Coins
The coins are modeled on a design created in Marseille, France, around 2,175 years ago. HS2

Archaeologists have been surveying sites along the HS2 railway’s planned 150-mile route since 2018, as Esther Addley reported for the Guardian near the start of the effort. Discoveries made by the controversial project include evidence of early human settlements from as long as 11,000 years ago. Other finds from more recent eras include a battlefield from the 15th-century Wars of the Roses and a World War II bombing decoy. Last year, archaeologists in Buckinghamshire found the probable remains of an Iron Age murder victim.

“HS2’s unprecedented archaeological program has enabled us to tell the stories of our history and leave a lasting legacy for future generations,” says the project’s head of heritage, Helen Wass, in the statement.

PA Media reports that the newly discovered coins may be recognized as treasure under British law. A coroner will determine whether they should receive that designation, which would clear the way for the potins’ acquisition by a museum. Already, the Birmingham Museum and Art Gallery has cleaned and preserved the coins.

“This is a once in a lifetime find, and allows us to expand our knowledge of what life could have been like in Hillingdon many centuries ago,” Tetlow says.