An exceptionally rare Celtic gold coin has been discovered by a metal detectorist in a corn field in Denklingen, Bavaria. The so-called “rainbow cup” coin is decorated with a cross design in the center of the bowl-shaped coin. Only four rainbow cups with these markings (including this one) are known to exist, and this example is the only one with a verified find location.

The coin dateS to the 2nd century B.C., a time when the Celtic monetary economy was still new. The gold examples were so rare because they were expensive to produce and were not in wide circulation. More common copper and silver versions have been found all over southern Germany.

They are called cups because they were struck in a rounded shape, unlike the more familiar flat circular coins of other ancient (and modern) cultures. They got the rainbow monicker because they were often discovered after rain washed away the soil leaving the proverbial pot of gold at the end of the rainbow glittering on the surface.

It’s unknown how the 0.07-ounce (1.9 grams) coin ended up there, but the spot isn’t far from a ancient road. This road went from what is now Trento in northern Italy and later became known as the Roman road Via Claudia Augusta that went across the Alps, Ziegaus said.

“Perhaps the coin was accidentally lost along the way,” he said.

The “heads” side of the 0.5-inch-wide (13 millimeters) coin “shows a stylized human head with a large eye,” with the nose and lips depicted as dots, Ziegaus said. A metal analysis revealed that the coin is 77% gold, 18% silver and 5% copper.

There are only three known rainbow cups with the star-and-arch motif. “The interpretation of the motive is difficult,” Ziegaus said. “The star is perhaps a symbol for the four cardinal points, the arches are to be understood as signs for the horizon and the rising and setting of the moon.

Until recently, even finds of archaeological significance like this coin were held to be shared property of the finder and landowner. A new cultural patrimony regulation just went into effect that requires archaeological finds be reported to the State Office for Monument Preservation. Bavaria is now the owner of the material. The landowner receives appropriate compensation and the finder receives a finder’s fee.

The finder, Michael Schwaiger, was offered 6,000 for both coins, but he refused, as well he should. The landowner signed his rights over to the finder and Schwaiger donated both coins to the State Archaeological Collection. The other three known rainbow bowls are in private hands, and state officials plan to exhibit the Denklingen coins in a new permanent exhibition at the State Archaeological Collection in Munich after renovation of the facility is complete in March 2024. They are unlikely to go on display at a local museum in Denklingen because the theft of the Celtic gold coin hoard from the museum at Manching has left officials very wary that they can be adequately secured.