J - 220 : The "Steely" Roman Empire

Segmented Plate Armor (Lorica Segmentata) weighted about 15 kilograms per Legionnaire

Global trade is made possible by maritime transport. These days, there are a good 107’000 merchant ships plowing the waves. Oil tankers account for about 12’000 ships, bulk carriers (ore, coal, grain) make up 13’000. There are 21’000 large cargo and 6’000 container vessels. The other 50% are smaller, primarily coastal merchant ships.

A Roman Grain Freighter leaving a Port - possibly Leptis Magna in today's Lybia

When writing my piece about Roman harbors ten days ago, I wondered how many merchant ships were cruising the Mediterranean in Roman time. I remember that the grain trade which supplied Rome with 400’000 tons of wheat p.a. required 1’000 to 1’200 ships. But I have not found any research on the total number of merchant ships. There must have been many. Maybe 5’000? Wine, olive oil and fish sauce were bulky goods and amphorae in which they were transported heavy. The average size of a cargo vessel was  200 – 300 tons. It could carry up to 6’000 amphorae. The Turkish built 30-meter-long Goulets we used for sailing for the last ten years are 250 tons. In any case, the number of vessels must have been large.

Roman Nails used for the Building of Commercial Vessels. Their weight varies from 15-30 g

I discovered how Romans built so many ships so efficiently when writing up the history of Forum Julii, today’s Fréjus on the Côte d’Azur. The Roman leader Julius Caesar did not trust Marseille and picked a new location for his naval base. He looked for a site with easy access to timber. Roman ships needed oaks for the ribs and keel, pines and firs for the planks and masts. To expedite the building process, Roman shipbuilders used iron nails. Not the wooden joints we find on Phoenician and Dorian (Greek) vessels. Several experts estimate that a medium size cargo vessel needed 2’000 – 5’000 nails. A large one 5’000 – 10’000. These nails were 5 – 7 inches long and weighted one ounce each (28.5 g). Thus, one ship needed 0.3 tons of iron nails. The whole merchant fleet 1’500 tons.

Photographic Reconstruction of Roman Dry Docks found recently in the Harbor of Ostia

The shipping industry was not the biggest user of iron and steel. Rome was the first “steely” empire. The total annual steel and iron production amounted to 75’000 to 80’000 tons per year. Iron ore mining was big business and happened primarily in Spain, Austria and the British Islands – one of the reasons Rome wanted to control these territories. The workers in the mines and smelters were slaves, mostly prisoners of war.

Greek Slaves in a Silver Mine in 5th Century BC - Roman Slaves worked in same Condition

Their working conditions must have been terrible. Except for small oil lamps there was no light underground. The mines were damp and always at risk of collapse. Water intrusions happened frequently. The slaves working the smelters were exposed to poisonous fumes. Life expectancy for slaves in the mining business was four to five years.

Entrance to a Roman Iron Mine - the Carriage Tracks are still visible

Today, we are so used to the use of steel that we hardly notice when we see it. Steel is in cars, buildings, weapons, cutlery, food processing and now even in Elon Musk’s Spaceship.

The Evolution of Roman Body Armor over the Centuries

In Roman time, Legions needed a lot of steel and iron. A Roman sword (gladius) weighted 1 kg per piece. Roman chain body armor (lorica hamata) about 10 kg and segmented plate armor (lorica segmentata) close to 15 kg. The total amount of steel (for the swords) and iron (for the body armor) for all Legions combined was 250’000 times 10 – 15 kg or 2’500 to 3’750 tons. Whilst these numbers are big, they could easily be produced by the private-public enterprises running mines, smelters and furnaces – often located close to the Legion’s headquarters.

Most Iron Clamps have been "mined" and removed in the Middle Ages. Why making Iron when you can get it from the Ruins of the Coliseum?

Romans also used a lot of steel in public buildings. Not for structural support and ceilings – they used their famous arches to support tall structures – but to stabilize high walls. Where they uses big stone blocks, they linked them with iron clamps for additional stability. The Coliseum alone used 350 tons of steel clamps. Agriculture was also a big user. Horses needed horse shoes and cart wheels iron “tires”. Last but not least, iron ware and steel weapons were one of Rome’s main export products. People outside Rome loved these products for their durability and strength. We find these items in archeology digs in Africa, India and Northern Europe.

Interconnected Water Pumps in a

Roman Mine in Spain

From today’s perspective, iron and steel consumption in the Roman Empire was modest. It amounted to 1.5 kg per capita per year. Global steel consumption today is around 220 kg. China with above 635 kg is an outlier – so is Africa with 40 kg. Today’s level of production is only possible with the application of huge amounts of energy which was yet unavailable to Romans. Steam technology and electricity were unknown at the time. Roman production was entirely manual – with significant division of labor – but manual. From chiseling ore from the mine’s veins to pumping water out of the shafts, all was done manually. The same was true for smelters and furnace. Charcoal was also produced manually. Air pumps for achieving heat of 1’200 degrees Celsius were operated by slaves or mules. The forging of steel from iron though was done by skilled labor. It took years to train a blacksmith to fuse carbon into iron, folding an iron rod again and again to achieve the properties which make steel so valuable – hardness and high flexibility.

Roman Mine in Las Medulas in Spain - here the Rock covering the Iron Ore was washed away by large Quantities of Water

Being able to produce large quantities of steel made the Roman Empire exceptional. Its steel production was 15 times higher than in contemporary Han China. Steel was one of the secrets of Roman might. Steel swords gave it battlefield supremacy, allowed it to build more ships faster and construct public buildings that nobody else could. As always, technology advantages fade. Technology is always imitated by competitors. Unless the innovative edge is preserved, other powers catch up. No empire lasts forever. It took until the industrial revolution though to get back to Rome’s steel production levels

.Distribution of Mines in the Roman Empire - They were primarily in the Western Provinces