A valuable ancient commodity: Miltos of Kea

By Effie Photos-Jones

The island of Kea in the North Cyclades is by some travel agents’ reckoning the (rich) Athenians’ ‘best-kept secret’, their beautifully-designed stone-built villas merging seamlessly with the barren landscape overlooking the blue Aegean Sea (Fig 1).

Fig. 1 Private house in Orkos, looking east. To the SE on can see the island of Kythnos. (c) Effie Photos-Jones

The scenery is even more spectacular in the south and in the east of the island. Although sparsely populated today, this area was from the mid of the 19th century and well into the early part of the 20th century, a hive of activity, on account of the extensive underground workings of the seams of lead and iron ores. Today, miners’ cottages stand derelict, perhaps waiting for a buyer to convert them into holiday homes. But the ground underneath Petroussa, Orkos or Trypospilies (Fig 2 map) is riddled with galleries, some dating as early as the 4th century BCE. These early galleries were opened with one aim in mind: to access miltos (Fig. 3c).

Fig. 2. A map of Kea with its four ancient city states and the miltos names Orkos, Petroussa, Trypospilies. (c) Effie Photos-Jones

The material they called miltos is a composite one consisting of naturally fine iron oxides (hematite/goethite) with small amounts of calcite, quartz and clay minerals. It made its first appearance in the Bronze Age Linear B clay tablets  as mi-to-we-sa. The Mycenaeans, acutely aware of colours, had many names for red, miltos being, we think, a red with a deep purple hue. It would be many centuries before Kea miltos would surface again in the literary record, always as the colour red but also as a whole host of materials whose colour merited that name. In the 4th century BCE Theophrastus (On Stones, 52) tells us that builders and joiners used it to draw a line with, workers in shipyards used it for ship maintenance and if the miltos came from the island of Lemnos, then it was used as a medicine, as well, and against ‘poison’.

From the above it is clear that miltos was a valuable commodity. But how valuable? An Athenian decree carved on a marble inscription found in the Athenian Agora and dated c. 360 BCE tells us exactly how valuable. The decree was issued by Athens to all the three city states of Kea (Ioulis, Korisseia and Karthaia (Fig. 2) requiring each one of them to export miltos in its entirety from their respective mines, exclusively to Athens; also for the Keans to bear the charges for the transport and only in an Athenian boat! The tone is severe and the penalties dire. The decree appears to openly invite a slave to denounce his master, if the latter is suspected of selling his miltos to a third party. It stipulates that the slave would be gaining not only his freedom but would also receive half of his masters’ estate!

Another contemporary inscription, more informative than severe, also from Athens mentions miltos mixed with pitch, the miltopissa. And at an even later date (3rd century CE), the author of an agricultural manual, recommends miltos for pest control. It suggests miltos should be smeared around the roots of trees ‘to prevent trees and vines from being harmed by worms or anything else’.

So what was the rationale behind all these diverse uses of miltos? was it a case of ‘since we have it …we might as well use it!’ or did antiquity have a more subtle understanding of this valuable natural material which has so far eluded us? We have been investigating….

As was mentioned miltos consists of very fine iron oxides with particle sizes ranging in the nanosized range. There are also impurities of lead, zinc, copper and arsenic within. But beyond its mineral components, Kean miltos also had an organic load. By that we mean microorganisms like bacteria, fungi and other which live around miltos, are feeding on miltos and also alter the environment around it (Fig 3). We became aware of these microorganisms through DNA sequencing of the miltos samples. Given that red Kean miltos was never heated but used in the ‘as was’ state it is almost certain that these microorganisms would have been carried along with the minerals. When the microorganisms died, they would release biomolecules (secondary metabolites), many of which are known to have numerous beneficial properties, as antibacterials, antifungals, antioxidants or other.

The diagram below (Fig. 4) gives a schematic illustration of the dual nature of Kean miltos, as a combination of both a biotic (microorganisms and biomolecules) and an abiotic (elements, nanoparticles, minerals) component.  It is the ‘intersection’ between the two components that gives rise to miltos’ diverse applications.

Fig. 4. Miltos’ diverse properties deriving from their biotic and abiotic components. (c) Effie Photos-Jones

When miltos is mixed with resin or pitch and applied on wood it is the toxic trace elements within which would inhibit the growth of deleterious biofilms. The same mixture could be used as pest control, by preventing the growth of microorganisms/ insects threatening tree health. If on the other hand, when miltos was mixed with water, the toxic trace elements within, mostly insoluble, would have little effect. Instead, it would be its biome, in the shape of bacteria which help the growth of plants, by making nutrients bioavailable at the root level, which would render miltos a good fertiliser. In short, each application appears, to have called upon and with confidence, either the biotic or abiotic component of miltos depending on the ‘problem’ at hand. No wonder the Athenians were taking no chances with the Keans and their miltos.

We have for long considered miltos a good and ‘special’ red pigment. But all along, it has been way more than that. The Athenians had made a shrewd assessment of this natural material and as an all-powerful city state they imposed their might on their allies. With the demise of the Athenian hegemony in the region, the importance of Kean miltos faded only to give prominence to that of Cappadocia traded through its Black Sea port of Sinope (Sinopic miltos).

Further Reading

Lytle, E. (2013). Farmers Into Sailors: Ship Maintenance, Greek Agriculture, and the Athenian Monopoly on Kean Ruddle (IG II 2 1128). Greek, Roman, and Byzantine Studies, 53(3), 520-550.

Photos-Jones, E., Cottier, A., Hall, A. J., & Mendoni, L. G. (1997). Kean Miltos: The well-known iron oxides of antiquity. The Annual of the British School at Athens, 92, 359-371.

Photos-Jones, E. et al. (2018). Greco-Roman mineral (litho) therapeutics and their relationship to their microbiome: The case of the red pigment miltos. Journal of Archaeological Science: Reports, 22, 179-192.

Effie Photos-Jones

Glasgow, UK

EPJ is a Senior Honorary Researcher at the University of Glasgow at the Schools of Humanities and of Earth and Geographical Sciences. She has been researching the metals and industrial minerals of the Greco-Roman world for over 40 years and more recently their pharmacological applications