A Working Battery With Nothing To Power

Wilhelm König was working through a shipment of finds in the storeroom of Baghdad's National Museum in 1938, objects pulled two years earlier from Khujut Rabu, a low mound of ruins near the ancient city of Ctesiphon, when one clay jar made him stop. König, the Vienna-born archaeologist running the museum's laboratory, realized this one didn't belong with the rest. Most of what came out of that site was ordinary: pottery, coins, the debris of a vanished settlement. This jar held something else. Inside its neck sat a cylinder of rolled copper sheet, sealed at the bottom with a soldered copper plate. Suspended inside the cylinder, held by a plug of asphalt so it never touched the copper walls, was a rod of iron.

König recognized the shape. Strip away the clay, and what remained was the internal anatomy of a simple electric battery: two different metals, kept apart, ready to sit in a liquid. He published the observation that same year, in a two-page paper whose title translates as "A Galvanic Element from the Parthian Period?" The question mark was doing real work. König had a hunch, not proof.

Later tests bore the hunch out. Fill the copper vessel with an acidic liquid available anywhere in the ancient world (vinegar, wine, even grape juice) and the jar produces a small, genuine electric current. Every replication since has confirmed it, most recently a January 2026 study that found a second, previously unnoticed cell hiding in the design itself: the jar's own unglazed clay, damp against a strip of solder on the copper's exterior, forming a separate battery in series with the first. Together they measured over 1.4 volts, enough to visibly electroplate metal or split water into bubbles of gas.

Ten broadly similar jars turned up nearby at Seleucia and Ctesiphon in the years after. Same clay body, same sealed metal tube inside. Not one of them had an iron rod.