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Comment by mabbo | Hacker News Reader

I suspect steel making was one of those pieces of knowledge that got lost frequently. The reason: it's incredibly expensive, in terms of energy requirements.

I have read that Roman legionaries, covered in armor, took acres of wood per soldier to make the charcoal needed to make the steel using traditional methods. Entire regions could be deforestated to outfit an army.

Technology is the story of better access to energy and information over time. Steelmaking requires both, and 2900 years ago we had very poor access.

Edit: as Luc pointed out below me, that figure is just for iron armor. Proper steel requires higher heat and even more energy.

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"To put that in some perspective, a Roman legion (roughly 5,000 men) in the Late Republic might have carried into battle around 44,000kg (c. 48.5 tons) of iron – not counting pots, fittings, picks, shovels and other tools we know they used. That iron equipment in turn might represent the mining of around 541,200kg (c. 600 tons) of ore, smelted with 642,400kg (c. 710 tons) of charcoal, made from 4,620,000kg (c. 5,100 tons) of wood. Cutting the wood and making the charcoal alone, from our figures above, might represent something like (I am assuming our charcoal-burners are working in teams) 80,000 man-days of labor. For one legion."

Of course it's from https://acoup.blog/2020/09/25/collections-iron-how-did-they-...

That's where I read that! I had forgotten, but of course it was the delightful Bret Devereux.

Still, that was just for iron. Steel requires even more energy- higher heat I believe?

And better ore. And more of it. It was until the early 20th century, way into the industrial revolution, that iron production outpaced steel production by 9 to 1. Today it is the opposite, with simple iron basically impossible to get.

As I understand it, what we call “mild steel” is simple iron; there is practically no carbon in it. The difference with what we have today is mostly the lack of other impurities: no slag distributed throughout the metal, and no sulfur dissolved in it.

Iron cookware, as opposed to cast iron cookware, is not "basically impossible to get," is composed of iron and contains no alloys.

What we call cast iron today is also basically just low grade steel. Pure iron, as used 100+ years ago is simply not made anymore. Also, most of the steel used nowadays is recycled, one way or the other.

> Iron cookware, as opposed to cast iron cookware

Did you not see that? Cast iron cookware is not iron cookware. Iron cookware is still available, generally labeled "pure iron" and marketed to impart more iron into the food being cooked than cast iron cookware. Maybe your waving hand should take a rest.

It's not just about heat. Steel is an alloy of iron and carbon. The traditional way to infuse carbon into the metal was to place wrought iron ingots (that is, ones with almost no carbon, too soft for use) into a charcoal fire that was being starved of oxygen, for days. You had to regularly add more charcoal, which both provided the necessary heat and slowly seeped into the metal. As mobility of carbon is very low at low heat, most of the charcoal is wasted as fuel.

Around the same time, the Chinese had already figured out the much more efficient process of starting with cast iron (iron saturated with carbon, easy to make but too brittle to use), and heating and working it in a very oxygenated environment, burning out the excess carbon.

I think the Linz-Donawitz steelmaking process does not get enough credit sometimes for how much it changed steelmaking

> It reduced capital cost of the plants and smelting time, and increased labor productivity. Between 1920 and 2000, labor requirements in the industry decreased by a factor of 1,000, from more than three man-hours per metric ton to just 0.003.

If only they had implemented a small carbon tax to offset this.

So sixteen man-days of labour per legionary. And 924 kg of wood; if you get 30 tonnes of wood per hectare (this is a SWAG based on a quick google), that's about 300 square metres per legionary.

For 5000 legionaries, that's 154 hectares, which is about a quarter of the Presidio in San Fransisco, half of Central Park in New York, or a bit more than Hyde Park in London.

It's a lot, but it doesn't strike me as, like, a lot a lot.

An excellent point. I wonder how it compares with the material and labour resources involved in equipping a modern army.

I wouldn't be surprised if the man hours per equipped soldier its much higher in a modern army. If you account for all the individual bits and bops, plus vehicles and modern weapon systems. That would follow the trend from the last +100 years where the price tag for the individual soldier sky rocketed.[0]

[0]https://www.nbcnews.com/id/wbna21105586

The other interesting angle is if you measure it per population unit defended, on the basis the point of all the heavy equipment is the ability to win wars without having to call up a particularly large fraction of the population to fight in them (the Romans are also outliers in history for ruling a large population with a relatively small skilled standing army rather than mass conscription)

But still not convinced that comes out at lower cost than the Romans. Lucky we've got a bit more productive capacity not devoted to producing food and basic infrastructure than they did...

IIRC there's a long series on the acoup blog referenced elsewhere in this discussion, that deals with the logistics of moving and feeding an army in pre-modern times.

Tl;dr: When you're limited to beasts and wagons, the possible size of your army is severely curtailed. Also foraging for food (again, with beasts and wagons there's only so much food you can transport over any non trivial distance) puts a quite low limit on the size of an army you can have in an area.

IOW, the modern mass army enabled by conscription is also dependent on a modern logistics system to supply them.

I’m no expert, but it’s my understanding that modern war uses huge amounts of ammunition for suppressive fire.

This is true, but there are a lot more hours available now than then. Global supply chains mean a modern "legion" can draw from the labor of 8 billion people. Those workers live longer lives, and far far fewer of them are working in agriculture just to keep themselves fed. This is before factoring in their productivity -- an hour of 2023 globalized labor is presumably many times more productive than an hour of 500 BCE Roman labor.

Throw in the resources needed for ships, civilian and military, civil infrastructure and the like, and you see why there is so little forest left in the Mediterranean. Plus, those things have to be replenished and rebuild over time, so it is not a one off.

I think the main reason there is that those areas have been inhabited for so long, and that wood is mostly used for cooking and heating, uses which would eclipse military production. And don't forget clearing forests to make fields for agriculture.

The heating needs are usually regrowing. Agriculture is a thing, sure. The majority of the forests on the Italian peninsula was used up by the powera to be, from the Romans to the Venetians, was used for ships now lying somewhere on the sea floor. You can read up on the history of the Battle of Lepanto, the Venetian Arsenal and just how much wood was cut down for that fleet on the Venetian side not to speak of the Ottomans.

Having the logistics in place for these kind of things is among the main reasons the Roman were able to buiod their empire in the first place.

It's a lot for a preindustrial society that has a very low surplus economic output that can be collected and diverted into a military by taxes.

Also, the logistics of keeping the legion fed and quartered when it is resting, or campaigning look a lot like 'it eats the countryside bare, and the peasants unlucky enough to be in its path starve'.

Even in an industrialized society, how many families do you know that would be able to quarter and feed, say, three to six soldiers for the four months break that they take from winter campaigning?

The real problem is that the Mediterranean islands had forests,

Forests that evolved in a similar way to the outstanding current Asian temperate forests that are a hot spot of temperate biodiversity. They were the home to endemic conifers, "italojapanese" maples, dwarf European elephants and rodents like bunnies with teddy bear ears.

All gone now. We will never know how an European "Asian jungle" would look.

I strongly suspect this is why half-timbered houses, although being much more earthquake resilient than stone houses, haven't been common in Italy for thousands of years now. There simply wasn't enough wood left.

And almost no old castles, palaces or significant ruins in flat and rock-less areas like west pomeranian in Poland. Bricks and stones were so valuable, that any abandoned stone/brick building was dismantled immediately for material for new buildings.

Only half of a legion was deployed in battlefields at any given time. So call it eight man-days per legionnnaire to outfit a legion, which is nothing in the era of slavery. Add to this that the equipment would be expected to last the 20 years that Roman served in the legion, and it looks pretty good

> might have carried into battle around 44,000kg (c. 48.5 tons) of iron

I suspect there were no Roman legions exactly fully equipped. Swords and weapons were probably far more popular than armor. And it's not like they discarded this stuff; it would be collected and redistributed possibly for generations.

> Technology is the story of better access to energy and information over time. Steelmaking requires both, and 2900 years ago we had very poor access.

Yes - and the modern industrial revolution involved a particular kind of "takeoff", as the iron and steel could be used to make steam engines which made mine pumping and ventilation easier, enabling more coal to be extracted to make more iron. Likewise in the modern era advances in oil drilling. It's all EROEI (energy return on energy invested).

The natural resources renew at a comparatively limited rate. Before cheap coal, Scotland was denuded of trees; WW1 also caused a historical low point in European forest cover.

This is why the transition away from fossil fuels before access to them starts getting too much more difficult is so important.

> Technology is the story of better access to energy and information over time.

This is an under-appreciated fact of history. Wealth and prosperity closely track the availability of cheap energy, which is why interfering with energy production in the name of supposedly higher goals is such a high-stakes gamble.

"We’ve gone from spending 4% of GDP on energy to spending 14% - a 10% loss straight away to just keeping the lights on, money that could be spent doing other things we care about, including energy." [0]

[0] https://climatepodnotes.substack.com/p/its-energy-stupid

A related fact is that sometimes “advanced technology” really just means using more energy. A simple tech example is the escalating thermal budgets of CPUs. Yes, if you let them draw more power, they can run faster. In my view, that’s a less interesting technological development than an innovation that allows more work to be done with less energy, or that unlocks previously inaccessible energy. Those are the type of inventions that truly qualify as an advancement.

> A related fact is that sometimes “advanced technology” really just means using more energy.

I don't think this is what generally happens. Chips right now do this because Dennard Scaling / Moores Law are coming to an end, so they have to increase performance in different ways to win some dumb benchmarks. Nearly everywhere else its the opposite. Cars, fridges, heating, houses, lighting - they all use less energy than they used to.

Jancovici's conference about how ecology and economy eventually boil down to fundamentals such as energy is eye opening:

https://www.youtube.com/watch?v=KtQBPhKSWu0&list=PLMDQXkItOZ...

The punchlines are wonderful. E.G: "The first law of thermodynamics will always win over political promises".

Highly recommended.

Some of his conferences and courses (in particular the École des Mines 20h course) are available with English subtitles.

Do you have a link?

Here you go:

Dubbed videos (mostly English but also Russian and maybe other languages): https://www.youtube.com/playlist?list=PLMDQXkItOZ4JcKrdHyRaA...

Videos with English subtitles: https://www.youtube.com/playlist?list=PLMDQXkItOZ4II_sYvh0Be...

Thanks.

The first one is French dubbed in russian. If you speak russian, I would recommend it as it as the slides clearly in view.

However, the second one, in English doesn't show most of the slides, and they are really necessary to get the full picture. However, it's a playlist, and there are better ones in there.

If you don't mind, I will update my comment to include one of them.

The process to make iron also resulted in a small amount of steel. You would have to outfit a couple legions in armor just to get enough steel for one sword, and then you have to collect that iron which might not have already been done. Thus the legendary swords that could cut armor like it was butter: if you collected all that steel your could make such a sword, but not many.

I remember NOVA did an episode "Secrets of the Viking Sword" (a sort of sequel to a similar episode about Japanese sword making traditions) where a modern blacksmith created a sword using presumed methods from the viking era to create a crucible steel sword. They pointed out the advantages that the better metallurgy would provide; I remember them showing the sword flex while most contemporary swords would have broken.

The idea was that this was sort of a trade secret for steel production and so it was rare and this may be one of the sources for legends of "magic swords".

No doubt it took a great deal of wood; this is also one of the reasons Pennsylvania in America developed a metallurgical industry. Plentiful wood for charcoal (this was before they started using coal, which Pennsylvania also had in abundance)

However I just want to point out that an acre really isn't that big. A single typical Roman fortification could easily cover tens of acres just inside the walls. "acres of wood" isn't really saying much.

Wow, thanks for visualizing this so vividly. I've never thought about it, but this is probably one more reason why Europe is as deforested as it is.

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