In nature, chemicals are hardly ever pure. No wedding ring is pure gold, and no natural water is pure. Copper ores are never pure either, and all smelted copper contains impurities. The ancient smiths who exploited the first easy native-copper nuggets, and the dramatically colored surface malachite and azurite carbonate ores could select relatively pure ores for their smelters, and they did not have to worry too much about impurities in the copper that they produced. But as demand rose and the first early ore discoveries were worked out, they mined deeper, and began to reach copper sulfide ores that were more difficult to smelt and less pure.
The "copper" that began to come from the smelters now had relatively more impurities in it. Smiths were inadvertently smelting batches of metal that were not pure copper. Each batch was now an alloy, a metallic substance that is not a chemical compound, but a physical mix of two or more metals that may act as if it were a different metal. In our modern hardware stores, for example, we can buy solder (an alloy of tin and another metal [often antimony] which doesn't behave like either of them).
Almost all copper ores contain some small proportion of arsenic, tin, zinc, antimony, or nickel, which mixes at the molecular level with the copper during smeltingin other words, a tremendous number of subtly different alloys can emerge out of a smelter after a mixture of ore has been smelted, even though the geologist has been skilled enough to select ores that are rich in copper. The alloys are still dominated by copper, but the alloy has a lower melting point than pure copper, which allows easier melting and casting. The castings are better quality, and the alloy is much harder than pure copper after it has been worked by hammering. Paradoxically, the less pure copper ore that was available, the greater the variety of alloy the smith would produce from his smelter. By trial and error, early metallurgists (smiths) would soon come to associate a particular mixture of ores in the furnace with a particular result. In time, a skilled smith would be able to have some control over the end product, producing not copper, not a random unknown alloy, but a specific alloy to suit the job at hand. The Bronze Age marks the time at which smiths became metallurgists, makers of magic, heroes, and gods. Bronze Age smiths were often buried with the tools of their trade: hammers, an anvil, knives and molds.
Bronze is any alloy that is 85-95% copper, with the other 5-15% made up of mainly of tin or arsenic, though other metals can be present in small amounts. It turns out that this range of chemistry produces an alloy that is harder than copper even though it melts at a lower temperature. A low amount of tin or arsenic does not improve the copper enough, and a higher amount makes the alloy so brittle that it is useless. Tin bronze is not too difficult to work, and melts at 950 degrees C rather than the 1084 degrees C of copper, making it easier to cast. Both bronzes make strong hard tools and weapons that retain an edge as well or better than stone, once they are strengthened by hammering. Other metal alloys were not available to bronze-smiths. Zinc (which alloys with copper to make brass) or nickel are rarer and much more difficult to smelt, and antimony/copper alloys are brittle.
In the Chalcolithic period in which copper and stone artefacts co-existed, we can see smiths producing bronzes, without realizing what they had done, and without using the bronze to its best advantage. For a long time, smiths used copper of greater or lesser purity without much discrimination. For example, many early Chalcolithic objects are made from copper with more than 5% arsenic. They were not made with the properties of arsenical bronze in mind, however, because there is no correlation between the object and the arsenic content: tools are made with low-arsenic copper and ornaments are made with high-arsenic copper. Probably arsenical copper was used only because arsenic lowered the melting point and made casting easier.
When and how were the mechanical properties of bronzes deliberately produced by smiths? I expect that at first, a skilled smith would be able to sense the different properties of each batch of metal that came from the smelter, and would keep the rough ingots arranged by property. He would quickly find that bronzes varied in hardness along a scale, with the optimal balance between softness and brittleness at 510% tin/arsenic. It's not that he had a chemical analysis, but he had a feel for hardness as he hammered the hot ingot. Once he was that far into the analysis, it would be an obvious step to combine two ingots at the ends of the scale to try to mix them into the best-quality alloy in between, and he would discover that the process worked as long as he melted then together completely. From that point, the smith with the best analytical skills (his touch with the hammer) would be able to produce the best artefacts.
At some point, a smith would connect the properties of the bronze ingot with the properties of the ores going into the smelter, which would save him a lot of work and charcoal blending ingot together. At this point the smith is truly master of his craft, and one can easily imagine that the best smiths would have routinely produced bronzes of much higher quality than normal. Smiths take on legendary or god-like form for the first time.
Arsenic ores are more common than tin ores, and make high-quality bronzes: there are no tin bronzes in Western Asia before 3000 BC. Arsenic bronzes do not cast as well, but are as hard as tin bronzes. The choice between arsenic and tin bronze may not have been easy, even when it became available. The choice may have depended on the ores available locally: arsenic/copper ores are common, while copper/tin ores are rare. We don't know accurately how often arsenate ores occur in copper deposits because the question is not important in modern mining. In this case, it is just possible that Chalcolithic miners were better informed than we are!
After 3000 BC, Cretan and Western Mediterranean bronzes were largely made with arsenic, Egyptian bronzes almost exclusively with arsenic, but Anatolian bronzes were made with both. We suspect that Anatolian bronzes were first made with tin extracted from the mineral stannite. It is difficult to distinguish tin-bearing stannite from the arsenic-bearing minerals arsenopyrite and enargite. Possibly the first use of tin ores stemmed from a simple mistake by prospectors searching for more arsenic-bearing ores.
Eventually smiths turned to tin ores even though they were more difficult to obtain than arsenic-bearing ores. Smelters work outside, so fumes can be dispersed in the wind, but a smith cannot help breathing in arsenic fumes as he heats, casts, and hammers hot arsenic-laced bronze. The symptoms of low-level arsenic poisoning develop slowly, usually over a period of years. The most obvious symptoms are gradual nerve damage in the limbs. Eventually smiths must have realized what was happening to them, and what was responsible; and eventually they recognized the danger of working with arsenic alloys. Except in Egypt, where arsenic was used until 2000 BC, tin bronze gradually became the alloy of choice, and the dominant metal of advanced civilizations in the Western World for 2000 years. The long agony of so many Bronze Age smiths has come down to us in legend, however: the Greek smith god Hephaestus and his Roman counterpart Vulcan were lame. This is not an occupational hazard of the Iron Age smiths that forged spears for the Greek hoplites and swords for the Roman legionaries. It reflects the centuries-old folk memory of their predecessors.
Bronze gave its name to the Bronze Age, a major innovative period in human history. Bronze artefacts are found at Ur and other Mesopotamian cities after about 3000 BC, then all over the Near East. A "bronze age" can only occur where copper and tin are both available, where the mining and smelting technology are developed, and where trade networks can disseminate the new technology and the new artefacts. Many regions did not have a bronze age, but changed directly from Chalcolithic to iron use.
Cassiterite, the dominant tin ore, is tin oxide. It occurs as distinctive black grains in alluvial sands, and in some areas it is left behind as a resistant mineral after granite has weathered down to sand and clay. It is possible that its properties were examined closely by potters: kaolinite deposits often occur around old granite bodies, and cassiterite grains could be caught up in potters' clay. Since cassiterite melts at only 600 degrees C, it would be noticed, and perhaps accidentally smelted to tin.
An ancient tin mine was discovered in the Taurus at a site named Göltepe, which was a large village from around 3290 BC to 1840 BC. The mine has narrow steep shafts, and at least some of the underground work may have been done by children (several skeletons of children have been excavated from the mine). Cassiterite ore was then crushed at the surface, washed, and smelted with charcoal in rather small crucibles rather than the large furnaces characteristic of copper smelting sites. Goltepe has yielded many crucibles in which the tin was smelted into a slag that contained globules of pure tin, which had to be separated out by crushing and re-washing. The small scale of the crucible operations, and the crushing of the slag for multi-stage refining, make it difficult to detect the scale of the operations. But since over time the industry produced enormous deposits of slag in the district (600,000 tonnes in one pile), Göltepe was probably a major site for much of the Early and Middle Bronze Age. Some of the slag may date from more recent times, at least some of it is ancient, and some of it is very rich in tin.
The Taurus mountains, then, probably provided the tin for alloying into the earliest tin bronzes of the ancient Near East. There is no copper at Göltepe, and the tin was clearly exported to other centers for making bronze. However, other cities close by were centers that were famous for metal trading and metal working in the second millenium BC: Kültepe and Acemhüyük.
The metal-working found in the royal tombs of Sumer (about 26502500 BC), whether it was done locally or was imported, is breath-taking in its beauty and skill. Riveting and soldering were invented, and by 2500 BC the value of tin was well known for soldering and brazing. Casting techniques were good enough to make human-sized statues and small lost-wax figurines.
Metal began to play a part in international relations, especially during Akkadian times (23502200 BC). About 2350 BC Sargon of Akkad invaded Anatolia from his lowland base. He set up a short-lived empire of secure trade routes, and he boasts that a single caravan carried about 12 tonnes of tin, enough to make 125 tonnes of bronzeand to equip a large army.
After the fall of Akkad, the Assyrians ended as the dominant power in what is now northern Iraq. We have known for a long time that tin was brought in to Kültepe, in Anatolia, by Assyrian merchants and sold to local metal workers at prices that are recorded on local tablets as very high. A major trade in tin is recorded in Old Assyrian letters from about 1950-1850 BC. Tin shipments were sent on donkey caravans from the Assyrian capital, Assur, to Assyrian merchants living in Kültepe, who sold it to the local smiths, presumably for bronze-working in and around Kültepe. The shipments record well over a tonne of tin per year, enough to make about 1015 tonnes a year of bronze.
This trade is subject to several interpretations, of course. The most likely is that foreign tin was imported to the processing area as local ores ran out, in the same way that South American tin was shipped to South Wales after the Cornish tin mines could no longer supply enough to the tinplate industry. (Today the British steel industry depends on imported iron.) Probably tin, the smaller and scarcer component of bronze, was shipped into Kültepe because the district was rich in copper, fuel, and technological skills, even after local tin ores were mined out. This policy would certainly make economic sense for the smiths of Kültepe, even if they had to import the tin to keep their bronze industry going. Presumably the Assyrians bought much of the bronze, though this is not recorded in the letters: the tin was sold in Kültepe for silver or gold. Kültepe by this time may have been very much a "smokestack" city, working bronze but with the profits skimmed off by the politically dominant Assyrians. (The letters indicate that the tin was marked up 75100% between Assur and Kültepe, while transport costs were about 10% of the price in Assur.) Certainly any wealth from the industry did not support the same glittering power at Kültepe that is seen often in Bronze Age centers, though the Assyrian merchants in Kültepe were buried with gold and silver ornaments!. By 2000 BC Kültepe was an industrial city: political power was elsewhere.
Tin must have been a very important strategic metal, even though bronzes could also be made with arsenic, at great occupational hazard for the smelters and smiths. All around the Mediterranean, copper and tin mining were dramatically stepped up in this period.
The Timna workings are some of the best-studied industries of the Early Bronze Age, typical of the entire desert copper-mining and smelting operations, even though the quantities mined were small, even by the standards of the time. The miners at Timna were digging for nodules of malachite in fairly soft sandstone. They used hafted stone hammers, digging vertical shafts connected by galleries. The shafts and galleries were rather haphazard, presumably following rich ores without any overall plan. The ore preparation sites contain broken pieces of malachite copper ore, granite mortars and pounding stones, other stone tools, and pottery shards. The smelting furnaces were not on the valley floor, but high on the ridges, so that the wind would help raise the furnace temperatures by forced draught. Pieces of slag are scattered round the furnaces, some containing little blobs of metallic copper created in the furnaces. The furnaces themselves are bowl-shaped, with a clay layer lining a sandstone cavity about 80 cm (nearly 3 feet) high. The fuel was collected from the desert acacia trees in the region, and fuel shortage was probably the main reason for the rather small production from Timna.
Experiments show that the Timna furnaces reached temperatures between 1180° to 1350°, which could only have been achieved with some forced draught other than natural wind currents. Perhaps goatskin bellows were used. Charcoal makes a hotter fire than wood, and may have been used also. The Timna furnaces produced rather impure masses of metal that needed further cold working by hammering, or a further firing to produce much purer copper ingots. (Later technology, with larger furnaces and hotter fires, allowed smelting to be carried out in one step.)
At Fenan, which was mined for copper in Chalcolithic times (Chapter 3), Bronze Age workings began around 2000 BC. The Fenan miners now followed the ores far underground, in inclined shafts that were as much as 15 to 20 m underground and at least 55 m long. The ore-bearing layers were carefully mined on a chamber-and-pillar system, with pillars left to support the roof. The best ore was separated from waste rock underground by lamplight, and the waste either packed into old galleries, or piled up into artificial support pillars, with the addition of large boulders dropped down from the surface from the bed of the wadi. These methods exploited the ore efficiently, avoiding the labor of carrying too much material up out of the mines.
Bronze Age production at Fenan has been studied only superficially. Fenan production was large, and it must have been a strategically important area. The copper was eventually worked into very finely executed objects, many of them ornamental pieces that presumably had high value. Copper objects were traded and hoarded at this time all over the region from Anatolia to Egypt and Mesopotamia.
The smelting centers nearby were highly organized, with areas for ore crushing, storage pits for ore, charcoal, and iron oxide flux. Scores of furnaces were clustered close together, this time on the valley floor rather than on the ridges, because the Egyptians now relied entirely on bellows to pump air through the furnaces. Each furnace was sunk into the desert sand, and was lined with cement. Each had one or more complex tuyères in it, nozzles to which a bellows were connected.
The copper was sent off to Egypt to be made into bronze: tin bronze by this time. Copper and tin ingots were melted together in the right proportion, and the molten bronze used to make the desired objects. These were sometimes as large as temple doors. The Sinai mines were not the major source of copper for ancient Egypt, however: there was extensive trade with Cyprus, too.
Once smelting of sulfide ores became economic from about 1600 BC, Cyprus became a vital link in the trade of Eastern Mediterranean Bronze Age cultures for 500 years, serving not just as a convenient island in the center of many trade routes, but producing large quantities of copper for export. Every major copper body mined in the early 20th century in Cyprus had already been discovered and mined in ancient and/or classical times. Altogether, Cyprus has more than 40 slag heaps containing more than 4 million tonnes of historic slag, showing the massive scale of the industry over time.
Homer says that his heroes wore Cypriot bronze armor in the Trojan War (about 1100 BC?). The Cypriots used copper and bronze to pay debts and tribute: for example, about 1470 BC the ruler of Cyprus paid tribute to Pharaoh Tutmose III with 108 ingots of copper. The ingots weighed about 30 kg (65 pounds), and were poured into molds that resemble ox-hidesa rectangle with four projecting corners. The size of the ox-hide ingots means that furnaces had reached much larger size than those at Timna a few centuries before: the ingots are ten times as big. The shape is probably convenient for pouring and handling, rather like the "pigs" of later iron-workers, but it may also refer to the bull-worship of the region. Ox-hide copper ingots have been found all over the Mediterranean shoreline, reflecting two facts: first, that most large-scale trade was shipborne; and second, that copper ingots were an acceptable form of currency. A shipwreck from about 1300 BC, discovered at Ulu Burun, near Cape Gelidonya on the Turkish coast, was carrying a tonne of copper ingots and several dozen small tin ingots, new bronze tools, and scrap metal, and a blacksmith's forge and tools. Thus the cargo of one ship could have equipped the army of one of the small Mycenean city-states: 50 suits of bronze-sheathed armor, 500 spear points, 500 swords. This ship was also carrying enough valuable gift goods (ivory scepters, shell rings from the Red Sea, and a complete ostrich egg) that excavators are beginning to suspect it may have been carrying a diplomatic mission along with its cargo of strategic weaponry (probably not a new concept in international politics).
Copper and bronze were precious enough that old artefacts were recycled. (A Middle Babylonian document says that if a slave escaped with his copper chains, the guard responsible would be charged twice that amount in copper. In other words, the chains were valued as much as the slave.) Smithies were often as much recycling centers for old bronze tools as they were centers for alloying new copper and new tin into bronze. Archeological sites often contain as much scrap bronze as they do new ingots.
Bronze became widespread in the central plain of China in early Shang times. The Shang dynasty ruled from its capital at modern Anyang, in Henan province, for 300 years until its collapse in 1122 BC. Anyang was close to the most abundant deposits of lead, copper, and tin in China, and bronze-making apparently spread from here to the rest of China. Shang metallurgists had discovered that a small percentage of lead in the bronze made casting easier. They produced ceremonial cast bronze cups and bowls of all sizes up to massive cauldrons, intricately decorated with raised or incised relief designs taken from nature. The largest Shang cauldron weighs 875 kg (nearly a ton), and is the largest metal casting from anywhere in the world from the second millenium BC.
Casting large objects is not easy. It requires large crucibles and efficient furnaces, and casting the largest objects requires coordinated melting in many crucibles that resembles a modern factory.
A problem with the quality of the Shang bronzes is that they are so impressively large, leading some scholars to feel that somewhere else there must be an earlier bronze-working culture still to be discovered. However, the Shang metallurgical tradition probably arose very quickly from pottery making. The Chinese made porcelain in Neolithic times: pottery kilns found near Xi'an were designed to maintain temperatures as high as 1400 degrees C as early as the 6th millenium BC, more than enough to melt copper. Many of the ritual Shang cups and crucibles, including their ornamental relief, are shaped in direct continuity with earlier clay objects. Shang metallurgists did not use stamping, or engraving, or hammering in their work: they simply cast their works of art. Probably, then, the Shang used casting methods almost exclusively because their pottery industry was so advanced they could readily reach the high sustained temperatures that made smelting and casting comparatively easy. The Western tradition of hammering metalwork and the Chinese tradition of casting it (at least from Shang times onward) are in stark contrast. .
The Chinese became more sophisticated bronze metallurgists than their Western counterparts. The famous terracotta army of the Emperor Qin, made for him about 220 BC and buried with him, have weapons that are basically bronze, but they have been deliberately alloyed with metals such as titanium, magnesium, cobalt, and so on, no doubt after empirical trial and error, to give superior hardness and penetrating power. This weaponry, combined with technological advances such as fast-loading crossbows, united China under the Qin dynasty and defended it against invaders.
Other Chinese bronzes, designed for other purposes, have lead alloyed to improve casting fidelity and to make polishing easier. These alloys were used to make bronze mirrors and bells. In 1978, 64 bronze bells were found in the tomb of a nobleman named Yi, dating from about 450 BC. The largest bell weighs 203 kg (about 450 pounds), and is 1.5 m (over 4 feet) tall. The bells together allow a complete 12-tone scale to be played by a team of five to seven musicians.
Overall, the Chinese bronze industry was very large: an enormous mine dating from around 400 BC has been excavated at Tonglushan: it covered an area of 2 km x 1 km, and had deep timbered underground galleries.
As cities developed around the seasonally dry eastern Mediterranean, they had to build large cisterns for water supply; most often their construction demanded large quantities of cement and plaster. Mediterranean private and public buildings all contained large quantities of cement, plaster, brick, and terracotta, all of which required far more wood for production than the equivalent amount used directly for construction. The effects on local fuel supplies would have been increasingly severe.
Egypt, which has practically no trees, was trading with Byblos (on the Lebanese coast) for cedar for shipbuilding, temple construction, and furniture-making as early as 3000 BC. But perhaps the most famous documentation of the shortage of wood around the ancient Mediterranean is the Epic of Gilgamesh, the earliest epic poetry that has survived. Gilgamesh was a Sumerian, king of Uruk around 2700-2500 BC. He conquered Kish, Uruk's great rival city, thus gaining power over all of southern Mesopotamia. Apparently the first epics about him were written in Sumerian around 2000 BC. We do not have the originals, but we have copies made by scribes in Old Babylonian times for their libraries. They were separate stories, and the welding of these separate pieces into an Epic was an Akkadian literary innovation, not a Sumerian one. This means that the central theme of the Gilgamesh epic may date to 1500 BC rather than Sumerian times, but it is still illuminating.
Stripped of sex and violence, the Gilgamesh epic is about deforestation. Gilgamesh and his companion go off to cut down a cedar forest, braving the wrath of the forest god Humbaba, who has been entrusted with forest conservation. It's interesting that Gilgamesh is cast as the hero, even though he has the typical logger mentality: cut it down, and never mind the consequences. The repercussions for Gilgamesh are severe: he loses his chance of immortality, for example. But the consequences for Sumeria were even worse. It's clear that the geography and climate of southern Mesopotamia would not provide the wood fuel to support a Bronze Age civilization that worked metal, built large cities, and constructed canals and ceremonial centers that used wood, plaster, and bricks. Most timber would have to be imported from the surrounding mountains, and deforestation there, in a climate that receives occasional torrential storms, would have led to severe erosion and run-off. The loss of Gilgamesh's immortality may be a literary reflection of the realization that Sumeria could not be sustained.
Theodore Wertime suggested that massive deforestation of the eastern Mediterranean began about 1200 BC, for construction, lime kilning, and ore smelting. Probably it began earlier in the drier regions further east. King Hammurabi's laws (around 1750 BC) carried the death penalty for unauthorized felling of trees in Mesopotamia. The problem may have been even worse in intensive metal-working regions like Anatolia. Metal smelting and forging had been going on in Anatolia for at least 3000 years by 1200 BC.
At any rate, most likely the Bronze Age saw a westward spread of a timber crisis. By 800 BC an extensive new use (ornamental and roof tiles) added to the burden, and around 500 BC the rise of the classical civilizations brought the final intolerable strain on the forests immediately round the Mediterranean. Eratosthenes, writing of the Late Bronze Age, say 1200 BC, reports that Cyprus was so heavily forested at that time that even smelting copper and silver, and felling trees for shipbuilding, had made little inroads on the forest. Farmers were even encouraged by gifts of land to clear the forest for agriculture. But soon after this a boom in mineral production, and a major improvement in the technology of tree-felling tools (as well as military weapons) both allowed and encouraged major forest clearing.
The great silver mines of Laurion, near Athens, required not only the fuel to smelt the ores, but the fuel to build and maintain the water cisterns. Wertime estimated on the basis of 3500 tonnes of silver and 1.4 million tonnes of lead production for classical Athens over perhaps 300 years, that the Laurion mines had consumed 1 million tonnes of charcoal and 2.5 million acres of forest. It is, in fact, quite likely that the mines declined, not because they were exhausted of ore, not because the miners had reached the water table, but because the fuel costs had risen to the point that they were uneconomic to run. It is clear that deforestation, accompanied by soil erosion, was already a severe problem in Attica, the region surrounding Athens. Plato wrote that the region is
a mere relic of the original country.... What remains is like the skeleton of a body emaciated by disease. All the rich soil has melted away, leaving a country of skin and bone. Originally the mountains of Attica were heavily forested. Fine trees produced timber suitable for roofing the largest buildings: the roofs hewn from this timber are still in existence.
Shipbuilding timber had to be imported from the Balkans and southern Italy to build the great Athenian fleet that beat the Persians at the Battle of Salamis in 480 BC. Timber was a vital strategic commodity during the Peloponnesian War between Sparta and Athens. In 422 BC the Spartans conquered the Athenian trading cities on the coast of Macedonia. This alarmed the Athenians greatly, because it cut off their gold supplies and their ship-building timber, which had been shipped down the coast from the inland forests of Macedonia. By 415 BC Alcibiades of Athens was arguing for a major expedition to try to seize control of Sicily because of the supplies of timber thereand the failure of this expedition was the critical point at which Athens lost control of the war and went down to defeat.
[A similar situation faced the British during the war against Napoleon. Napoleon had ordered an embargo on trade with the British, and in 1801 the French armies controlled Denmark. The Danes controlled seaborne trade with the Baltic Sea, because all ships had to pass by Copenhagen on their way out through the Kattegat into the North Sea. The Baltic trade was vital for the British because it provided them with their only supply of fir trees for ships' masts for the Royal Navy. (The American colonies, with their vast forests, had been lost in 1783 or 1776, depending how you like to count it.) The British fleet bombarded Copenhagen, destroyed the Danish fleet, and opened that vital strategic route. History might have taken a very different turn if the British had failed. It was close. Admiral Nelson ignored orders to withdraw (by putting his telescope to his blind eye) and pressed home the critical attack on the Danish fleet.]
The crisis in wood continued to plague Athens. By 313 BC the only available ship timber in or close to Greece itself was in the far northern forests of Thrace and Macedonia: overseas supplies had to come from the Black Sea coasts, southern Turkey, Lebanon, or Italy. By the 4th century BC it was no longer economic to transport charcoal overland and uphill to the mines at Laurion: instead, the ore was smelted down on the coast, and charcoal was shipped in on barges. Even then, an increase of lead content in the slag shows that the smelting was being done with minimum fuel.
The island of Elba was once called Aethaleia, "the smoky island," because of the massive smelting industry there. But the Romans had to give up smelting ores from Elba on the island itself in the first century BC because they ran out of wood: they had to ship ore to Populonia on the mainland to continue the industry. By late medieval times, even the productive forests of Germany could usually support iron smelting for only three months a year.
The Rio Tinto mines in Spain probably needed 260 tonnes of wood a day even in Roman times. Fuel shortage may have been the single most serious constraint on copper production as early as the Bronze Age in some areas.
Copper smelting needs a great deal of fuel, especially if the ore supply is dominantly sulfide. About 300 kg of charcoal are needed to produce 1 kg of copper by smelting 30 kg of sulfide ore. A tonne of charcoal needs somewhere between 12 and 20 cubic meters of wood.
Archaeologists have estimated that the Bronze Age copper mines at Mitterberg, in the Austrian Tyrol near Salzburg, must have employed about 180 miners and smelters to produce about 20 tonnes of copper a year. Then one has to add the woodcutters, carpenters, charcoal burners, and carters who cut, carried, and processed the wood needed for the gallery timbers, the firing of the working face, and the fuel for the furnaces, and then add the farmers that fed all these. This was a very large-scale operation.
In copper smelting we find, perhaps, the first major environmental effect of mining. The Mitterberg copper mine probably required about 19 acres of forest to be felled each year, just for the smelters. Even with efficient natural regeneration of the forest, this is a sustainable harvest from perhaps 2 square miles of forest. In fact, however, the cleared land was probably used not for re-growth but at least partly for agriculture, to support the mining community.
On a time scale longer than 10 years, however, a Bronze Age copper mining operation must have caused local deforestation on a large scale, and ever-increasing costs for hauling the wood to keep the industry going.
The problem may not have been so great in the Alps, where there were smaller populations, and where the forest regrew comparatively quickly. But in the drier Mediterranean countries, there was an irreversible change in the vegetation and landscape. On Cyprus, the magnificent pine forest that once covered the island was cleared in a comparatively short time, mainly for charcoal for smelting. Cyprus has a classic Mediterranean climate with a long dry season, and winter rains on steep deforested slopes quickly degrade the soil by washing it downhill. Seedlings have difficulty in re-establishing the forest, especially after clear-cutting, and the soil quickly degrades to the point that pine forest cannot recover even by deliberate planting. Certainly the Mediterranean island of Seriphos has been deforested for a long time, although there are large copper slag heaps on the tops of the ridges, evidence of former forest and former massive wood consumption.
The tremendous tonnage of ancient copper slag on Cyprus suggests that the Cypriot copper industry collapsed around 300 AD simply because the island ran out of cheap fuel. The slagheaps suggest a total production of perhaps 200,000 tonnes of copper, and that in turn suggests that fuel equivalent to 200 million pine trees were cut to supply the copper industry, forests 16 times the total area of the island. Even given that high-altitude Cypriot forests can regenerate quickly in the right conditions, this suggests that wood fuel was a critical constraining factor on the Cypriot copper industry, and must have been a persistent problem on the island for other industries too.
The landscape of Cyprus today (and Greece, and Turkey, and Lebanon, and in fact most of the Mediterranean seaboard) is quite unlike its appearance 5000 years ago. The magnificent cedar forests of Lebanon were felled largely for timber for buildings and ships, but copper smelting must take most of the blame in Cyprus. This Mediterranean ecological disaster used to be blamed on the Arab introduction of goats to the region several centuries AD, but the change was much earlier. There are secondary effects of deforestation, of course: hillsides are exposed to greater run-off, and erosion can be greatly accelerated. Part of the story of the later Bronze Age seems to be the silting of coastal ports and cities. The city of Tiryns, for example, spent a great deal of effort just before its end building a diversion structure to keep floods out.
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