> In July 2014, we conducted a survey of Pompeii’s street network to document traces of iron that were observed on the stone-paved streets, which resulted in the identification of 434 instances of solid iron and iron staining among the paving stones. ... Pompeians were—in addition to using solid iron wedges—pouring molten iron and iron slag onto their streets as a method of emergency repair.
There's a huge gulf of difference between "a civilization is capable of melting iron" and "molten iron is so cheap and easy they used it to fill potholes".
Castable iron: Valuable, scarce, energy intensive, very hard to melt (comparatively), corrodes readily (especially on the coast)
Iron and other metal slag: Byproduct of iron smelting, basically waste, melts fairly easily, was used as ballast in ships, comparatively cheap, rusts superficially but is mostly a matrix of oxides which don't meaningfully react
I'm beyond skeptical that perfectly good cast iron was used to fill potholes. Using slag/dross/failed smelts/other byproducts of metallurgy makes far better sense.
It would be like far future archeologists unearthing rammed earth tire walls and concluding "the 20th century was so efficient at producing rubber they used excess tires as a building material" vs "they used a waste product which would have been landfill anyways".
No iron melts in a bloomery; the slag is liquid and the solid bits of iron sink to the bottom of it. Blast furnaces melt the iron, but weren't found in Europe until much later than the eruption of Vesuvius (China was just getting them around this time).
I am somewhat sceptical, as iron was very expensive back then. And they do not come up with a working idea how they possibly could have done it in an economic way. Portable smelters were not really a thing. And building an oven next to every hole does not sound too practical either. At least not easier, than just fixing the holes with stones.
Also shouldn't we have found other instances, where it was done?
"The researchers found that repairs using liquefied ore were being carried out just before the city’s destruction."
So my first (uneducated) guess would rather be, that hot lava might have tampered with the evidence.
I also thought "hang on a minute. Pompeii? As in volcano Pompeii?" but apparently the city was never flooded with lava, but rather ash, which was cooler than would melt iron (still fatally hot though).
Even with Lava, you're not going to melt iron, even when' it's just leaving the volcano it's not generally hot enough, and by the time it reaches the city it's even colder.
The melting point of iron is very high, and that's why for a long time iron was never molten even during the production process (slag was, but not the iron)
Also from the Wikipedia, I learned that people died of the heat and not suffocation. Which means that episode of Stargate lied to me where they claimed the opposite.
A multidisciplinary volcanological and bio-anthropological study[53] of the eruption products and victims, merged with numerical simulations and experiments, indicates that at Pompeii and surrounding towns heat was the main cause of death of people, previously believed to have died by ash suffocation.
The eruption was a violent explosion with molten rocks flying around. Some of them probably hit the city and some of them contained lots of iron would be my guess.
You do get some very large deposits of mostly pure iron, all of which in Europe would be fully mined out by now. Here's a mine in Northern Canada near my own which has 60-70% pure iron ore (truly astronomically high purity compared to ores for other metals).
The most pure type of iron ore is magnetite (Fe3O4). Magnetite contains the highest iron content among the common iron ore types, with approximately 72.4% iron content. It's still an oxide that requires extraction though...
Elemental iron on Earth is extremely rare due to the oxidizing atmosphere. It is found either in meteorites, or so called telluric iron deposits (https://en.m.wikipedia.org/wiki/Telluric_iron), which is only found on Greenland, and was produced by iron ore getting accidentally smelted by magmatic processes.
The deposit contains 60-70% of iron atoms, in various iron oxides, silicates, oxides, carbonates, etc. It's not elemental iron. It has to be smelted to get elemental iron.
That's like saying seawater has 12.5% hydrogen. Technically true, but you need an awful lot of work to get that hydrogen into elemental form.
There are some known techniques to deoxidize iron from the medieval and renaissance periods, and they take a lot of work (and even more wood). Here's an EXCELLENT write-up for anyone curious, https://acoup.blog/2020/09/18/collections-iron-how-did-they-...
> Iron ores are rocks and minerals from which metallic iron can be economically extracted. The ores are usually rich in iron oxides and vary in color from dark grey, bright yellow, or deep purple to rusty red. The iron is usually found in the form of magnetite (Fe_3O_4, 72.4% Fe), hematite (Fe_2O_3, 69.9% Fe), goethite (FeO(OH), 62.9% Fe), limonite (FeO(OH)·n(H_2O), 55% Fe), or siderite (FeCO_3, 48.2% Fe).
> *There are some known techniques to deoxidize iron from the medieval and renaissance periods, [...].
I agree. To deoxidize iron you must heat it to a few thousand degrees and mix it with coal, so the carbon in the coal steals the oxygens in the ore and you get metalic iron. (I'm oversimplifiying, and ignoring a lot of details that I don't even know.) It's not easy and not cheap.
I thought early Earth had no free oxygen with which to oxidize metal until life started producing it as a waste product? Isn't that why the banded iron formations exist?
Banded iron formations are iron oxide, not elemental iron. Vast amounts of iron were dissolved in Earths oceans, until oxygen produced by photosynthesis oxidized it, to form iron oxide, which precipitated and sank to the bottom. This process went on for 2.5 billion years until all the dissolved iron was consumed.
> I thought early Earth had no free oxygen [XXX] until life started producing it as a waste product?
It's correct, but metal did get oxidized abyway before that. Don't expect to time travel and see bunchs of metalic Sodium.
I'm only 99% sure thre was neither metalic Iron. Anyway, I googled https://en.wikipedia.org/wiki/Banded_iron_formation The idea is that the water alewady had oxidized iron(2+) and some bacterias oxidized it to iron(3+) that is no so soluble and then you got deposits of mixed iron(3+), iron(2+) and oxygen (2-).
Elemental iron is in fact present in some rare geology on earth. However, that's unlikely to be related to this issue, since they found the iron localized to main roadways and not splattered all over.
But iron ore is. And TFA literally talks about "liquified molten ore".
And this is speculation, but I assume a molten ore rock from inside the vulcano shot outwards, might have enough energy and time to purify itself a bit (different elements have different density, centrifugal principle).
^F ore says no. This is the only mention of "ore" in TFA:
> In a way, the idea of using iron to fix potholes has come full circle. Currently, researchers in Minnesota are experimenting with using tailings left over from processing taconite, a type of low-grade iron ore, into a durable road patch.
I probably should get the actual paper, yes. The articles are not that great, one has to read between the lines, that they talk about iron ore and not pure iron. Or rather iron slag. The byproduct of melting.
But I meant the economics of getting the liquid iron (or slag) to the holes. If there were many furnaces nearby, maybe they just used that and carried it some meters, but longer distances?
This article is incorrect. The actual claim is that the romans were making repairs with molten ore, ie slag, which has a substantially lower melting point than molten iron and would be a cheap byproduct of iron production.
Unless I'm mistaken, this strikes me as a really incredible claim. To the best of my knowledge, Rome didn't make much use out of cast iron. Iron has a very high melting point, it's not something that people were just casually melting. There were a few exceptions, but my understanding is that Europe mostly didn't use cast iron until late in the middle ages.
The idea that some random resort town was casually melting iron and hauling it around to fill cracks strikes me as really implausible. Some other, more easily melted metal perhaps, but not iron. Not unless my understanding of Roman metallurgy is really mistaken.
I'm currently reading a book about Cleopatra [1] (it's superb) and I've been absolutely boggled by the productive capacity of the nation states of her era. Whether it was building ships, growing and transporting grain or raising armies, these were highly sophisticated bureaucracies that knew how to make, grow and transport huge quantities of stuff.
I'm at work and don't have the book on me, so I may have this slightly wrong, but IIRC, in Cleopatra's day Alexandria (where she resided with her court) was consuming 300 tons of grain per day, which arrived on ships via the Nile. Or consider the ability of Rome to draft and train legions of highly-skilled soldiers: it was at a scale similar to that of modern-day Russia.
I do find this quite hard to believe. Iron would be considered an expensive material to use in roadbuilding even today. The pictures aren't all that convincing.
> But lead author Eric Poehler of the University of Massachusetts Amherst writes that stray iron drops found on the street suggest that the molten metal was carried from a furnace to the repair site.
If the hypothesis is that they were capable of carrying molten metal from a furnace to the road, isn't it more likely that these are splashes or spills from molten iron en route to a blacksmith?
You say "even", as if the Roman empire wasn't on par with the western empire today. I disagree. Even though we're at the tip of the ice berg, the human history is episodic in a way.
> Remind me how many teraflops the most powerful Roman computer was capable of?
Bad metric. We could go to the moon in the 70’s, and had supersonic passenger planes, and we could build at scale.
Today California can’t build a train, building a nuclear powerplant takes 20 years and we can’t go to the moon and don’t have supersonic passenger planes. So we have partially regressed despite having more terraflops
"Can't" vs "won't" is a huge distinction. All the examples you provided are either economically non-viable, bureaucratic landmines, or believed to be pointless. You can argue whether those arguments are justified, but the point is we didn't forget the technology.
Indeed politics, culture and posturing can be strong incentives that change the economics balance.
If the Roman empire had one thing as advanced as our modern states that wasn't technology per se but the politics, the politicking the perverse incentives to do something to show for and a public whose murmur mattered.
If some city official decided to impress visitors with some smooth roads perhaps he found a solution that wasn't strictly the best economically but perhaps it had other advantages that helped him getting a promotion?
I think this is pure copium. It’s use it or lose it - if you ‘won’t’ and chose not to build nuclear reactors for 40 years, then wake up one day and decide to do it, you will find that you can’t.
Experience engineers will have retired or found other jobs. Knowledge is gone. The books have been lost, etc. If you haven’t been to the moon for 40 years, then you can’t any more. That’s two generations of people.
Ability is not like a statue that you keep in a museum. Even a car will not start after sitting the garage for 10 years. Organisations and people fall apart even faster.
> most of the streets in the bustling seaside city were paved with silex, a type of cooled lava stone
'silex' is a rather old-fashioned word; nowadays it's more commonly called 'flint', which is a sedimentary rock, not an igneous one. https://en.wikipedia.org/wiki/Silex
> processing taconite, a type of low-grade iron ore
taconite is typically 30%–35% iron, but it's true that most iron has historically been made from higher-grade ores than that (though throughout history iron has usually been made from lower-grade ores, just in much smaller quantities)
it is indeed fairly surprising to find cast iron in a roman town. china had cast iron from around 2500 years ago, but i thought the technology only reached europe during medieval times, and even later in western europe
Your Wikipedia link says: "The word silex was previously used to refer to flint and chert and sometimes other hard rocks." Seems this was a fairly generic word.
According to http://doi.org/10.3764/aja.122.4.0579 which is the paper this blog post was based on, "The paving stones of Pompeii consist of a heavy, dark basaltic lava stone, which we describe as 'lava stone,' or silex, using the general Latin term. For local travertine stones, we use the common name, 'Sarno limestone.'"
One of the authors of the paper wrote a book, The Traffic Systems of Pompeii, which has: "When covered in gravel or created in beaten earth, the surface was calld glarea, but when paved in harder stones, the term silex was applied."
yes, the ancients often erred in their identification of minerals, lacking things like the flame test and spectrometers, not to mention atomic theory
thanks for finding the reference from the paper! it's puzzling that the article would describe 'heavy, dark basaltic lava stone' as 'a type of cooled lava stone that wore away relatively quickly'. basalt is one of the more wear-resistant rocks
Huh, I would have bet $10 that flint was igneous. Given how glasslike it can be I thought it was related to obsidian.
Turns out it’s sedimentary, and I overlooked considering all the non-volcanic places it can show up naturally. I guess it’s time to brush up on my geology and mineralogy: https://en.m.wikipedia.org/wiki/Flint
> 'silex' is a rather old-fashioned word; nowadays it's more commonly called 'flint', which is a sedimentary rock, not an igneous one. https://en.wikipedia.org/wiki/Silex
From the start of the wikipedia link you yourself provided: "Silex is any of various forms of ground stone."
the next sentence says, 'In modern contexts the word refers to a finely ground, nearly pure form of silica or silicate' and then it goes on to explain that it historically referred to either flint or things that people confused with flint
So given that there are multiple things that it has meant over time, the first statement that it can refer to "any of various various forms of ground stone" seems like a good summary.
To claim it can only mean silicates, when two paragraphs later it says "Silex is now most commonly used to describe finely ground silicates", seems somewhat disingenuous. It's not "only used" but "most commonly used".
your attack on my integrity is outrageous and utterly uncalled for; it's entirely possible to disagree with people without insulting them, and i suggest you learn how right now
i don't think 'there are multiple things it has meant over time' is really correct, except in the sense that imperial roman mineralogy was entirely incapable of meaning things we mean today, because they lacked much of our conceptual framework. they didn't know the difference between basalt and flint, evidently, much as many people today don't know the difference between nylon and polyethylene and consequently mistakenly call their polyethylene shopping bags 'nylon'
Count me as skeptical as well. Not only would it have been wildly impractical, but iron is prone to rusting and expands when it rusts. Plus it is slippery when wet. It's just not a good pothole filler.
Also seems like the stone around it would wear more quickly and then instead of potholes you'd have iron bumps in the road, not much of an improvement.
I wonder if this was just the doings of some eccentric in an act of euergetism (the wealthy supporting their cities through public works and the like) who thought that iron was just the thing. It was a resort city that attracted a lot of rich folk. It seems possible that rather than giving us insight into how the Romans maintained their cities it is just unveiling some small interesting idea someone brought into reality.
It is unlikely we'll ever know for sure. But it is interesting to contemplate how much of what we think we know about the past could be just way off and we've invested too much into artifacts of odd occurrences that just happened to survive while the more mundane and "real" are lost to time.
That would have been astronomically expensive given the enormous supply chain needed to produce charcoal to get that iron in those times.
I am sceptical on how they figured out iron stains are pothole fillings. I think much simpler explanation would be everyday items or metal pieces of carts getting stuck between stones.
They lived in really nice villas too. Frescos on the wall and mosaic floors. Better constructed than modern ones in some regards. No sqeeky floors for example. Surrounded by organic gardens with lemons and oranges and fragrant spices
Badass article, super cool to think about filling pot holes with molten iron.
Visited Pompeii with family when younger and one of the few things I remember “experiencing” were the wheel ruts while walking around.
Very much makes sense now how difficult it’d be to fill in given the depth and width of the ruts; they’re expansive.
Am not familiar with iron making but curious about iron slag. Welding slag is pretty light but if iron slag was used for ballast it must be substantial
https://www.ajaonline.org/article/3863
> In July 2014, we conducted a survey of Pompeii’s street network to document traces of iron that were observed on the stone-paved streets, which resulted in the identification of 434 instances of solid iron and iron staining among the paving stones. ... Pompeians were—in addition to using solid iron wedges—pouring molten iron and iron slag onto their streets as a method of emergency repair.
There's a huge gulf of difference between "a civilization is capable of melting iron" and "molten iron is so cheap and easy they used it to fill potholes".
Castable iron: Valuable, scarce, energy intensive, very hard to melt (comparatively), corrodes readily (especially on the coast)
Iron and other metal slag: Byproduct of iron smelting, basically waste, melts fairly easily, was used as ballast in ships, comparatively cheap, rusts superficially but is mostly a matrix of oxides which don't meaningfully react
I'm beyond skeptical that perfectly good cast iron was used to fill potholes. Using slag/dross/failed smelts/other byproducts of metallurgy makes far better sense.
It would be like far future archeologists unearthing rammed earth tire walls and concluding "the 20th century was so efficient at producing rubber they used excess tires as a building material" vs "they used a waste product which would have been landfill anyways".