What orichalcum is, and is not
Orichalcum was a prized metal in Greek and Roman writing, and the name is best known today because of Plato’s Atlantis. It is not a lost super-metal. The best-supported reading is that the term was used for a copper-based alloy, probably some form of brass, and that its exact meaning shifted over time. The most important recent find is a group of ingots from a shipwreck off Gela in Sicily, announced in 2015, whose composition is a copper-zinc alloy. That discovery shows that such metal existed in the ancient Mediterranean. It does not show that Atlantis did.
The word and its early uses
The Greek oreichalkos is usually explained as “mountain copper”, from words for mountain and bronze or copper, though the etymology is not certain. The term appears in early Greek poetry, including the Hesiodic Shield of Heracles and a Homeric hymn to Aphrodite, usually as something bright and valuable. In these poems it is a poetic detail, and they do not explain how it was made.
By Plato’s time, in the 4th century BCE, the word had a mystique. That mystique matters for the next section, since Plato may have chosen a metal that his readers already associated with rarity and brilliance.
Plato’s Atlantis
In the Critias, one of the Timaeus and Critias dialogues, Plato describes the island of Atlantis as having walls covered in metals, with orichalcum coating the innermost wall so that it gleamed with a reddish light. He says it was dug out of the ground on the island and was valued second only to gold. He adds that in his own day it was known only by name.
This is the central point to hold on to: the orichalcum of Atlantis is part of a story told by Plato to make a philosophical point about ideal and failed societies. Whether Atlantis was based on any real event is debated, and the long list of Atlantis location theories has never produced a convincing candidate. Atlantis in Plato is a literary account with no independent evidence. Any metal in the story is therefore a feature of the story, not a clue to a place.
Later Greek and Roman writers
Later authors treated orichalcum as something real. The Roman natural historian Pliny the Elder, writing in the 1st century CE, discusses it as a copper-related metal that had once been mined but, in his day, was no longer obtained from the earth. He also reports that the Romans used a metal under this name for some coins.
That fits what is known of Roman coinage. After a reform often placed around 23 BCE under the Augustan principate, larger denominations such as the sestertius and the dupondius were struck from a yellow, brass-like alloy, while smaller ones used copper. Ancient writers called this metal orichalcum, and the practice shows how the word could be used for ordinary brass. In the study of coin minting, the contrast between yellow brass coins and reddish copper ones is a standard way to tell denominations apart.
Making brass in antiquity
Brass is a mixture of copper and zinc, and making it was not simple. Zinc boils at a low temperature and tends to vanish as vapour when smelted in an open furnace, so ancient metalworkers could not easily produce pure zinc. Instead they used a process often called cementation. They heated copper with zinc ore, usually in a closed crucible, so that zinc was absorbed into the copper. The technique is generally thought to have developed in the first millennium BCE, and it was widely used by Roman times.
It is a different path from bronze alloying, which combines copper with tin. Bronze was known thousands of years earlier, as shipwrecks such as the Uluburun shipwreck of the Late Bronze Age, with its copper and tin ingots, make clear. Brass appears to be a later, more specialised development.
The Gela ingots
In 2015, divers working with Sicily’s sea authorities recovered a cargo of metal ingots from a shipwreck close to the shore at Gela, in southern Sicily. The wreck is generally dated to roughly the 6th century BCE, about 2,600 years ago. Reports gave the number of ingots recovered at that stage as several dozen, and further ones were found later.
Analysis reported at the time found that the ingots were mostly copper, at roughly 75 to 80 percent, with about 15 to 20 percent zinc and small amounts of other metals such as lead, nickel and iron. Archaeologists described them as an orichalcum alloy, in the sense of an ancient brass. The recovery drew on the same underwater archaeology methods used at other wrecks, with surveys, careful lifting and later laboratory analysis.
The ingots are significant because they are physical evidence of a copper-zinc alloy moving as cargo in the Mediterranean well before Roman times. News stories often called it “the metal of Atlantis”, but that label was a headline, not a scholarly conclusion. The wreck belongs to a trading world, and nothing in it ties it to Plato’s island.
What can and cannot be said
Several claims can be made with reasonable confidence.
- Orichalcum was a real word for a copper-based metal in Greek and Roman usage.
- By Roman times, it very often meant brass.
- The Gela ingots are a copper-zinc alloy from around the 6th century BCE.
Other claims go beyond the evidence. There is no proof that Plato knew of a lost island with this metal, that Atlantis existed, or that the Gela cargo came from anywhere beyond the ancient Mediterranean trade. Scholars also debate whether Plato’s orichalcum was supposed to be brass at all, since he describes it as mined from the earth and tells us it was no longer known.