Ancient Greek and Roman records refer to a mysterious group of islands called the Cassiterides. These islands were a source of tin, an important product in the Greco-Roman world. Yet despite apparently being a major source of the metal, there is considerable debate today about where these islands were actually situated. Some researchers identify them with the British Isles, the Isles of Scilly, or islands closer to Spain and Portugal, but what do historical records reveal?
What were the mysterious Cassiterides?
The best place to begin is, logically, with the earliest records of these islands. The first surviving mention of the Cassiterides comes from Herodotus, a Greek historian of the fifth century BC. Regarding the western regions of the world, he wrote:
“As to the extremities of Europe towards the West, I am not able to speak with certainty: for neither do I accept the tale that there is a river called in Barbarian tongue Eridanos, flowing into the sea which lies towards the North Wind, whence it is said that amber comes; nor do I know of the real existence of the Cassiterides [or, ‘Tin Islands’] from which tin comes to us: for first the name Eridanos itself declares that it is Hellenic and that it does not belong to a Barbarian speech, but was invented by some poet; and secondly I am not able to hear from any one who has been an eye-witness, though I took pains to discover this, that there is a sea on the other side of Europe. However that may be, tin and amber certainly come to us from the extremity of Europe.”
Here, Herodotus does not tell us much about the Cassiterides. He merely notes that they were allegedly the source of much of the Greeks’ tin, though he himself appeared to doubt their existence. Hence, from the outset, we can see that mystery has always surrounded these islands. Even to the ancient Greeks, the Cassiterides were remote and enigmatic.
Where were the Cassiterides?
As we move forward in history, we find that Greco-Roman geographers appeared to have some familiarity with the location of the Cassiterides. Over time, these islands came to be widely accepted as real, and ancient references suggest that their location was thought to be established.
However, ancient geographers often confidently described places and phenomena that never actually existed. Even so, Strabo noted that a Roman general, Publius Crassus, had reportedly visited the islands. This is evidence that the Cassiterides were indeed real and accessible.
Strabo was among many ancient writers who situated the Cassiterides north of Iberia (modern-day Spain and Portugal). These writers described the Cassiterides as small islands, yet they were inhabited and were also a prominent source of tin. Strabo claimed that there were ten islands in this archipelago.
We know that Cornwall, in southwest Britain, was a major center of ancient tin production. This has led some researchers to associate the Cassiterides with the British Isles. However, that identification is problematic, as it does not align with the ancient description of the Cassiterides as small islands.
Another proposal points to the Isles of Scilly, an archipelago just off the tip of Cornwall composed of five inhabited islands and countless smaller islets and rocks. Yet this theory also has shortcomings in that these islands lack substantial tin deposits, and there is no archaeological evidence of extensive mining there in antiquity.
How Herodotus helps locate these islands
To determine the true location of the mysterious Cassiterides, or Tin Islands, we can examine Herodotus’ description more closely.
At first glance, it seems Herodotus offers little of value regarding the location of these islands. He merely places them in the far west of Europe. However, a more careful reading reveals he may have directly associated these islands with the Eridanos River. After expressing doubt about both the Eridanos and the Cassiterides, he explains his skepticism by noting that the name “Eridanos” is clearly Greek in origin, and that he was unable to find eyewitnesses to confirm the existence of a sea lying to the west of Europe, into which the Eridanos supposedly flowed.
The fact that he gives no specific reason for his doubt regarding the existence of the Cassiterides strongly suggests that his source directly linked the Cassiterides with the Eridanos. In other words, he was referring to a single tradition rather than two unrelated ones—one concerning the Eridanos River and the other the Cassiterides. If so, this would logically mean that the Cassiterides were in the sea into which the Eridanos flowed, probably near the mouth of the river. Is there a major river flowing into the sea west of Europe (but north of Spain, as per Strabo and others)?
The only possible candidate is the Loire, which flows into the Bay of Biscay to the west of France. Hence, Herodotus’ description logically places the Cassiterides somewhere in that area.
The true identity of the mysterious Cassiterides
A French scholar named Roger Dion published an explanation for the location of the Cassiterides in 1952. This theory was later taken up by the British scholar Gavin de Beer and is often regarded today as the most convincing. Interestingly, although it does not rely on the aforementioned evidence from Herodotus, it is entirely compatible with it.
The argument is that the Cassiterides were located in the Brière marsh area, just north of the Loire estuary. This region has silted up considerably since antiquity. In the past, there were distinct islands there. As Gavin de Beer explained:
“The islands and shores of this gulf, now joined by silt, are crowded with Bronze Age foundries that worked tin and lead.”
Therefore, the archaeological evidence strongly supports the conclusion that these former islands were the real Cassiterides.
Supporting evidence
This conclusion receives strong support from Festus Avienus. Writing in the fourth century AD, this Roman author drew on a much earlier Greek source. Based on that source, he described the rocky peninsula of Brittany in northwest France and the bay partially formed from it—evidently the Bay of Biscay.
Significantly, he then refers to a group of islands called the Oestrymnides, which were rich in tin. The context and even the name of these islands indicates that they must have been located near Brittany, where a tribe called the Ostimii once lived. Avienus never mentions the Cassiterides, despite describing the very region where they were allegedly located. This indicates that the Oestrymnides and the Cassiterides were in fact the same islands.
Therefore, Festus Avienus provides compelling support for the theory that the Cassiterides were located in the Brière marsh area, near the Loire estuary, just south of Brittany.
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