The Roman Empire and the Silk Routes

The Ancient World Economy & the Empires of Parthia, Central Asia & Han China

Raoul McLaughlin

• Publisher: Pen & Sword History
• Year: 2016
• ISBN:
  9781473889811
• Topic: History
• Subtopic: Roman Ancient History
• Index: History

A fascinating history of the intricate web of trade routes connecting ancient Rome to Eastern civilizations, including its powerful rival, the Han Empire.
 
The Roman Empire and the Silk Routes investigates the trade routes between Rome and the powerful empires of inner Asia, including the Parthian Empire of ancient Persia, and the Kushan Empire which seized power in Bactria (Afghanistan), laying claim to the Indus Kingdoms. Further chapters examine the development of Palmyra as a leading caravan city on the edge of Roman Syria. Raoul McLaughlin also delves deeply into Rome’s trade ventures through the Tarim territories, which led its merchants to the Han Empire of ancient China.
 
Having established a system of Central Asian trade routes known as the Silk Road, the Han carried eastern products as far as Persia and the frontiers of the Roman Empire. Though they were matched in scale, the Han surpassed its European rival in military technology.
 
The first book to address these subjects in a single comprehensive study, The Roman Empire and the Silk Routes explores Rome’s impact on the ancient world economy and reveals what the Chinese and Romans knew about their rival Empires.

CHAPTER ONE

Steel and Silk

The ancient evidence suggests that by the first century AD almost 50 million people out of a total world population of perhaps 250 million were under Roman rule.¹ During this era, the city of Rome was the largest urban centre in the ancient world with over a million inhabitants.² But Rome did not exist in isolation; there were large-scale economic connections between the leading Mediterranean cities and the commercial centres of Asia.

In ancient times many regions of the world produced unique products that were considered valuable commodities in distant markets. During the reign of the first Emperor Augustus (27 BC–AD 14) large quantities of foreign imports from Arabia, India and China became widely obtainable in Mediterranean markets as popular consumer goods.³ Amongst these eastern imports were incense from the southern Arabian kingdoms of the Saba-Himyarites in Yemen and the Hadramaut in Dhofar. These valuable fragrant resins were used in perfumes and burnt as religious offerings in Greek, Roman and Persian cultures. Indian Kingdoms provided spices that were much sought after and valued across the ancient world as flavourings for foods and ingredients in remedies. Other Indian products included precious stones, ivory, pearls, crystals and cotton. Most eastern ports adjoining the Indian Ocean also offered turtle shells that were carved into decorative objects by Roman craftsmen. Merchants, traffickers and consumers were prepared to pay large sums for these unique goods, and the regimes that controlled the production, or conveyance, of valuable commodities acquired longterm advantages in the ancient world economy.

In the Roman Empire eastern imports became synonymous with social prosperity, perceptions of male status and concepts of feminine beauty. Foremost amongst the unique products transported through eastern trade routes were oriental steel and durable Chinese silks spun from the thin protein strands of insect cocoons. Western civilizations did not yet possess the knowledge or skill required to manufacture these commodities, so the Romans had to rely on foreign supplies to fulfil their consumer demands. Silks and steel from China entered Roman Syria from Iranian caravan routes that crossed the Parthian Empire from Transoxiana (Uzbekistan) to Mesopotamia (Iraq).⁴ Oriental goods were also shipped from India through the Persian Gulf to reach Parthian markets in Babylonia (southern Iraq).⁵ This consumer demand encouraged international commerce and provided the finance for Roman trade ventures to distant lands beyond the previous limits of classical knowledge.

The Manufacture of Iron and Steel

Oriental steel had a significant value in distant markets since Roman workshops could not mass-produce metals with comparable strength and sharpness. Steel is a metal alloy manufactured by heating iron ore to high temperatures, then combining the molten metal with carbon or other strengthening elements. The grade of steel produced by these techniques depends on the sustained temperature of the furnace and the quantity and condition of the added compounds. Good quality steel is harder than iron and has much greater flexibility and tensile strength. Blades made from steel therefore maintain a sharper edge for a longer time and have a greater resistance to rust than their equivalent in iron.

Widespread steel technology would have improved the long-term prospects of Roman civilization by permitting the manufacture of more effective agricultural blades, construction tools, armour and weaponry. But imperial Rome lacked the expertise to mass-produce reliable steel as western civilizations did not have sufficient knowledge of the required carbon compounds that were added to the molten iron. Instead, the Romans produced wrought iron by first heating iron ore in a furnace to separate metal from waste slag in a process known as ‘smelting’. This technique was used throughout the Roman Empire to make tools and bladed weapons. The resultant iron also acquired a trace of strengthening carbon from the charcoal fuel. The cooling lump of soft white-hot metal was then ‘forged’ by being beaten and drawn into the required shape using hammer and tongs. During this process the iron was repeatedly reheated in a furnace to keep it malleable and ‘quenched’ in cold water to fix and harden the blade. Hence the name ‘wrought’ or ‘worked’ iron. Iron quenched in oil produced a more malleable metal that was suitable for hobnailing military sandals or providing metal rims for vehicle wheels.⁶ Roman military bases stored both hard and malleable iron along with charcoal to fuel the open hearth furnaces used by their armourers.⁷

A more costly and advanced method of iron manufacture was the production of ‘cast’ iron. In this process the ore was smelted in an enclosed furnace, but the temperature was increased until it melted into a semi-liquid state. The molten metal would then be poured into a mould to take the shape of the finished object. During the heating process the melting iron rapidly absorbed large amounts of carbon, so the finished ‘cast iron’ piece was hard, but relatively brittle. This meant that it was liable to crack or shatter under a heavy blow and could not be forged by reheating, or using hammer-strikes to modify its shape. The production of cast iron was rare in the Roman Empire due to the design of furnaces which could not easily produce and sustain the high temperatures required to convert the metal into the required molten state.

Wrought iron has a carbon content of about 0.5 per cent, while cast iron contains about 4 per cent carbon. Fine quality steel has a carbon value close to 1 per cent, which produces a metal that is sharper and harder than wrought iron. With this percentage of carbon content steel does not have the brittle structure of cast iron and can withstand heavy impact shocks. The problem for ancient metallurgists was therefore how to control carbon levels in the furnace so that the resultant iron had the qualities of steel. Sometimes Roman smiths would create a batch of iron with steel properties, but these were chance occurrences that were not easily replicated. Roman authorities recognised that ore from certain territories created better quality iron due to natural compounds in the slag material, but Roman metallurgists never learnt how to replicate this process and produce consistent steel from ordinary iron deposits.

The use of better metal components might have engendered important technological advances in classical society. For example, during the imperial era Greek engineers in Alexandria experimented with small steam-powered devices. In the first century AD, Heron of Alexandria designed a primitive steam-engine called an aeolipile that consisted of a brass sphere that could rotate on an axis and was fitted with outward pointing bent nozzles. Water was heated inside the sphere or fed into the device, so that pressurised steam rushed from the nozzles and forced the orb to rotate at speed.⁸ However, one reason why these contraptions could not be developed into more practical machines was the lack of suitable metal components.

The best quality iron produced in the Roman Empire was extracted from mountains near Noricum on the north side of the Alps. Elements of manganese contained in Noricum ore produced iron that had steel-like properties and consequently was in high demand across the Empire. Ovid refers to the famous strength of this metal when he describes desires: ‘harder than iron tempered by Noric fire’.⁹ Horace also mentions strong emotions such as pain and anger, ‘undefeated by Noricum swords’.¹⁰ He describes certain death as, ‘a leap from the highest tower, or your chest pierced by an Alpine blade’.¹¹ The Emperors recognised the value of these iron resources and Hadrian had the text ‘met[alla] nor[ica]’ placed on his coins. This was perhaps to celebrate an imperial visit to Norica, or the discovery of new ore reserves in the region (AD 134–138).

Noricum iron was used for axes, agricultural tools, chisels and stonecutting equipment while Roman doctors recognised that the sharp cutting edges of Noricum blades made superior tools for fine surgery. Galen devised a special instrument for dissecting spinal cord which was made from Noricum steel so it would not easily blunt, bend or break. He recommended these instruments for abortions, or removing a foetus that had died in the womb. The surgery required, ‘a straight one-sided cutting blade: blunt-pointed. Novacula or razor: blunt-pointed bistoury, ring-knife for dismembering the foetus’.¹²

Noricum iron ore was quarried at two ancient sites that were nearly 40 miles apart (Erzberg and Eisenerz in modern Austria). During the first century AD, metal production was concentrated at the nearby town of Virunum which was established as a municipium by the Emperor Claudius. The site of Virunum was near modern Magdalensberg and resembled a small Italian town with elongated tabernae (workshop-residences) facing the forum (central town square). Two smithies on the northern side of the forum had cellar storerooms which have been subject to excavation.¹³ Both cellars had business notices scratched into their plaster walls recording how bulk orders were assembled and collected by contractors from distant regions. Steel rings, iron disks and hooks were sold wholesale to visiting businessmen in batches of over 500 items. Some of these batches weighed over a ton when they were collected and transported from the site. One order included 115 anvils while another records the sale of 225 anvils to a single contractor.¹⁴ Many of these consignments were transported across the Alps into Italy where the nearest port was Aquileia on the Adriatic coast more than 120 miles distant from Virunum. Some consignments were destined for workshops in Northwest Africa and one of the buyers who visited Virunum several times was a man named Orosius, a citizen of Volubilis in Mauretania.¹⁵ The town of Volubilis (near Meknes in Morocco) was more than 1,200 miles from Virunum and 100 miles inland from the Mediterranean coast.

Other towns founded by the Romans were famous for their iron production, including Bilbilis in northeast Spain (near Calatayud). Bilbilis was 100 miles from the Mediterranean coast, but it produced and exported iron to other provinces. Martial was born in Bilbilis and he describes his hometown as ‘renowned for its mines of cruel iron’ and a place well-known for ‘resounding with the noise of metal-work’.¹⁶

The situation was different in the Han Empire where Chinese metalworkers using more advanced furnaces had identified the natural compounds that created better quality iron during the smelting process. Through continual practice they had refined the measurements needed to ensure that the compounds added to iron ore introduced sufficient carbon to create a reliable quality of steel. The Chinese had developed large enclosed furnaces and double-action piston bellows that used bamboo nozzles to produce steady streams of air. This made it easier to keep the fire at a steady heat and control reactions within the furnace. Chinese furnaces also burned coal cakes which further increased temperatures and reduced fuel costs. This was significant because mass-produced cast iron could be transformed into steel by applying blasts of oxidizing cool air to the molten metal (the ‘Hundred Refinings Method’). The Chinese also knew how to turn wrought iron into steel. Blades were wrapped in fruit skins rich in carbon containing a small amount of slag, charred rice husks and specialist powdered minerals. These packages were then sealed in clay crucibles and heated at high temperatures over a sustained period (up to twenty-four hours) until the metal absorbed the necessary carbon and strengthening elements. In China these techniques were used to mass-manufacture knives, hatchets, chisels, adzes, drill bits, hammers, ploughshares, hoes, spades, shovels, rakes, sickles, wheelbarrow axles, cooking pots, pans and kettles.

This important development allowed the Han regime to mass-manufacture high-quality metal including armour-piercing crossbow bolts. The Han understood that steel manufacturing techniques provided Chinese troops with superior armour and weaponry. Consequently, the regime tried to restrict the spread of this technology to foreign peoples and prevent the export of Chinese steel supplies to the Steppe nations.¹⁷ However, there were strong incentives for Chinese merchants to break the embargoes and offer steel at high prices to foreign traders. Smuggling became a problem and the warlike Xiongnu (‘Hun-nu’) people of Mongolia were able to capture Han metalworkers when they raided Chinese territory. From these prisoners the Xiongnu learnt how to produce supplies of their own steel weaponry which they offered for exchange with other Steppe peoples.¹⁸ In this way supplies of superior oriental steel reached the Parthian Empire in Iran.

The superiority of this steel weaponry was demonstrated on the battlefield of Carrhae in 53 BC when a legionary army encountered a Parthian battle-host from eastern Iran. The steel-tipped arrows carried by the Parthians easily punched through Roman shields and armour, and their steel lances were able to pierce through the entire bodies of the legionaries. On the battlefield, mounted Parthian cataphracts were protected by layers of steel-enhanced armour and they seemed to be impenetrable to javelin strikes and stabs from the short gladius swords carried by Roman infantry.¹⁹

The early Roman Empire possessed no weapons or armour comparable to that of the Parthians. Consequently, Roman authorities did not fully understand the significance of the metal used by their Iranian rivals. It was assumed that Parthian steel was the product of unique iron ores that could only be found in the distant east and no initiative was taken to try and determine how these metals could be produced. Pliny describes ‘Parthian iron’ as superior to all other ferrous alloys with the exception of the steel produced by the Seres or ‘Silk People’ (the Chinese). He explains that ‘of all the different types of iron, the Seres produce the most excellent variety and they send it to us along with their delicate fabrics and animal furs.’²⁰ This ‘natural resource’ explanation seemed reasonable when the Romans consider...