The Baghdad Battery, also called the Parthian Battery (Persian: باتری اشکانی), is an artifact made of a ceramic pot, a copper tube, and an iron rod sealed together with bitumen. It was found in 1936 in Khujut Rabu, Iraq, near the ancient city of Ctesiphon. This city was the capital of the Parthian Empire (150 BC to 223 AD) and the Sasanian Empire (224 to 650 AD). The artifact is believed to be from one of these time periods.
Its origin and purpose are unknown. Wilhelm König, who was the director of the National Museum of Iraq’s laboratory, suggested it might have been used as a galvanic cell, possibly for electroplating or electrotherapy. However, no objects from this time show signs of electroplating, and most archaeologists disagree with this idea. Another theory is that it was used to hold magic spells for protection, defense, or curses.
Ten similar clay vessels were found earlier. Four were discovered in 1930 in Seleucia during the Sassanid period. Three of these were sealed with bitumen and contained a bronze cylinder, which was also sealed. Inside were pressed papyrus wrappers with decomposed fiber rolls, held in place by up to four bronze and iron rods sunk into the ground. Their purpose is not fully understood. Six other clay vessels were found nearby in Ctesiphon. Some had bronze wrappers with decomposed cellulose fibers, while others had iron nails or lead plates.
The current location of the Baghdad Battery is unknown since the 2003 US-led invasion of Iraq.
Physical description and dating
Austrian archaeologist Wilhelm König described the discovery, as translated into English, as follows:
Inside a jar-shaped container made of bright yellow clay, the top had been removed. A copper cylinder was inserted into the jar and held in place with asphalt. The jar was about 15 centimeters tall. The copper cylinder had a closed bottom and was made from thin sheets of copper. It measured 26 millimeters in diameter and 9 centimeters in height. Inside the cylinder, a rod of iron was found. The iron rod was completely covered in rust and was held in place by a stopper made of asphalt.
König noted that the copper cylinder was "fairly pure copper with small amounts of zinc, lead, and iron."
The copper cylinder is not watertight. If the jar had been filled with liquid, the liquid would have surrounded the iron rod. The artifact had been exposed to the weather and had suffered damage from rust.
König believed the objects might be from the Parthian period, which lasted from 250 BC to AD 224. However, St John Simpson of the British Museum’s Near Eastern department stated that the original excavation details and the context of the discovery were not well recorded. This makes it difficult to support the claim that the items are from the Parthian period. Additionally, the style of the pottery matches that of the Sasanian period, which lasted from 224 to 640 AD.
Albert Al-Haik reported that the original findings from the 1936 excavation, led by Sherif Yousif and Jawad al-Saffar at Khuyut Rabbou'a, were located about two miles northeast of Baghdad, near the city’s eastern edge. W. B. Hafford provided more information about the discovery in a video response to Milo Rossi’s video on the topic.
Comparable finds
Similar containers, which can be identified mainly by what was inside them, were discovered and studied earlier:
In 1930, four clay vessels were found at Seleucia under the leadership of Leroy Waterman from the University of Michigan. All four were made of common, unpainted ceramic and closed with bitumen stoppers. Each was between 6 and 8 inches (15 to 20 cm) tall. Three of the vessels were placed horizontally and held in place by up to four metal rods at the ends and sides. These rods were 6 to 10 inches (15 to 25 cm) long, with one iron rod per jar and the rest made of bronze. Each of the three horizontal vessels contained a bronze cylinder, sealed at both ends. All three cylinders were the same size: 1¼ inches (3 cm) in diameter and 3 inches (7½ cm) long. Inside, the cylinders held plant material. One had decomposed into flakes, one had a small, tightly wrapped core, and the third contained a papyrus roll folded at the ends. The fourth jar was found upright and held pieces of a small, broken glass bottle. Silver coins found nearby suggest the vessels date to the Sasanian period.
In 1931, a German-American team led by Ernst Kühnel discovered six more clay vessels in Ctesiphon, a nearby location. This group included three sealed objects, each containing one, three, or ten wrapped and sealed bronze rolls. Inside the bronze wraps were badly decomposed plant fibers. Another clay vessel held three sealed bronze cylinders. In two other sealed vessels, there were plates of pure lead covered with lead carbonate, and in ten heavily corroded iron nails, traces of wrapped organic fiber material were found. These discoveries were also dated to the late Sasanian period.
Electric battery theory
The origin and purpose of the Khujut Rabu jar are still unknown. Wilhelm König worked at the Iraq Museum in the 1930s. He noticed many silver objects from ancient Iraq covered in thin gold layers and thought they might have been electroplated. In 1938, he wrote a paper suggesting the jar could have formed a galvanic cell, possibly used to electroplate gold onto silver. This idea is not accepted by archaeologists or scientists.
Two media reports from 2003 and 2004 claimed that tests on the jar’s metal corrosion showed an acidic substance, like wine or vinegar, might have been inside. However, these reports did not provide sources for this claim. In 1993, Paul T. Keyser suggested that the asphalt seal on the jar might indicate the presence of liquid. At the time, most known liquids were acidic, except for vegetable and mineral oils. He proposed that this liquid could have acted as an acidic electrolyte solution, helping create an electric current from the difference in electrode potentials between copper and iron.
Experiments
After an attention-grabbing article about the jar appeared in the March 1939 edition of Astounding Science-Fiction, electrical engineer Willard F. M. Gray at the General Electric plant in Pittsfield, Massachusetts, created a replica. Gray tested it using copper (II) sulphate solution as the liquid in the experiment. He said it worked well for a short time.
Arne Eggebrecht, a former director of the Roemer- und Pelizaeus-Museum Hildesheim, claimed to have used silver plating on a surface that was not named. He connected many copies of the jar together and used grape juice as the liquid in the experiment. This process only created a thin layer of silver, 100 nanometers thick. Bettina Schmitz, a researcher at the same museum, told BBC News that no written records of experiments from 1978 exist. She said there are no photos or documents about these experiments in the museum’s archives, and no one involved in 1978 could confirm details.
In 1993, W. Jansen described an experiment using diluted acetic acid mixed with dissolved benzoquinone in a container. He said the results of this experiment were promising.
During the 29th episode of the Discovery Channel program MythBusters (23 March 2005), the team built ten handmade replica terracotta jars to act as batteries. Lemon juice was used as the liquid to enable a chemical reaction between copper and iron. When all ten jars were connected in a series, the battery produced 4.33 volts of electricity. When linked in a series, the ten jars created enough power to electroplate a small copper token with zinc after being left overnight. Five jars produced a painful electric current through acupuncture-style needles placed on skin, but ten jars were not enough to deliver a shock through dry skin. Archaeologist Ken Feder, who appeared on the show, noted that no archaeological evidence has been found to support claims that the jars were connected (which would be needed to create enough voltage) or that they were used for electroplating.
Problems with the electrical interpretation
The iron rod extended beyond the asphalt plug, but the copper tube did not. This made it impossible to attach a wire to complete a circuit.
A 2002 article in Plating & Surface Finishing described what would happen if the jar were used for electroplating. If used as an electrical cell, copper would dissolve into the liquid, creating large amounts of copper salts in the ceramic vessel and copper metal on the iron parts. The jar was thought to be a battery, but another cell would be needed for electroplating. No evidence of an electroplating cell with gold or silver traces has been found.
König was likely mistaken about the objects being electroplated. Instead, they were probably fire-gilded using mercury. Paul Craddock of the British Museum explained that examples from this time and place show traditional gold plating and mercury gilding. No clear proof supports the electroplating theory.
König saw early gold electroplating in Baghdad in 1938 and thought the method might have been passed down by local jewelers. Gerhard Eggert found that the technique used by Baghdadi silversmiths in 1938 was nearly identical to a process invented in Birmingham, UK, in 1839 by John Wright. This process used a ceramic flowerpot.
David A. Scott, a senior scientist at the Getty Conservation Institute, wrote that many writers assume ancient objects from 2,000 years ago were used for electroplating. However, there is no evidence to support this idea for this region at that time.
Paul T. Keyser of the University of Alberta noted that using only vinegar or other available electrolytes, the jar would produce very weak electricity. For this and other reasons, Keyser concluded that even if the jar was a battery, it could not have been used for electroplating. However, Keyser still believed it was a battery, possibly used for mild electrotherapy, such as pain relief through electroacupuncture.
A bitumen seal, which is thermoplastic, would be very difficult to use in a galvanic cell. This type of cell requires frequent refilling of the electrolyte for long-term use.
Tests by Emmerich Paszthory showed that oxygen limited the cell’s function when the electrolyte was water mixed with salt, acetic, or citric acid. Sealing the copper cylinders, as seen in archaeological finds, stopped electricity production immediately.
Paszthory also found that when used as an electrode, an iron rod erodes at the neck. The tapered shape of the iron nail suggests it was not used as an electrode.
Wilhelm König noted that the jar closely resembled four others found in Seleucia and six in Ctesiphon. In 1932, Kühnel described the Ctesiphon jars as containers for "conjurations, blessings, and the like," possibly written on papyrus. Paszthory believed the Khujut Rabu jar and others from Seleucia and Ctesiphon were magic objects, as all parts were associated with magic at that time. The copper tubes likely held protective spells, and iron nails were used to secure the contents. Brad Hafford of the University of Pennsylvania and Penn Museum agreed with this analysis. The jars found in Seleucia were near three magical or incantation bowls made to protect against demons. Two of the bowls had fake writing and were stacked over an inscribed eggshell. The Khujut Rabu jar was also found near magical bowls.
The artifacts are similar to other objects believed to have stored sacred scrolls from nearby Seleucia on the Tigris.
In March 2012, Professor Elizabeth Stone of Stony Brook University, an expert on Iraqi archaeology, said she knew no archaeologist who believed these objects were batteries.