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Comment by londons_explore | Hacker News Reader

They don't show any large patch filling a rut.

Also, molten iron would have presumably been expensive back then - too expensive to simply pave a large part of the street with.

I don't really see evidence this was street repair as much as "occasionally on the roughest roads some drips of molten iron fell off the back of carts while being transported"

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They show a whole segment of street repaired this way.

But, as noted in the article, they didn't just fill holes with iron. They filled them with loose aggregate, and glued it all together and to the road by pouring iron over it.

Transporting molten iron by road (for some reason other than fixing the road) would have been even more silly then than it is now. How many molten-iron trucks have you encountered?

Molten iron is not commonly transported on a truck, but molten aluminum is trucked relatively often, with occasional spills.

https://i.imgur.com/Qkai24I.jpg

Aluminum melts at 660C where Iron melts at 1,538°C. This makes molten Iron vastly more difficult and dangerous to transport.

Steam explosions like happened in the UK steel yard recently.

And for comparison, here is what happens when a train carrying molten iron spills - http://i.imgur.com/qnHuxET.jpg

edit - I think the tree is doing suprisingly well, considering.

But why would someone need to carry molten iron? It is inconvenient and dangerous.

I'm pretty sure no one moves large amounts of molten iron today. With ancient technology it would have been impractical even if they wanted to, maybe impossible.

Have you seen https://www.quora.com/Why-is-molten-aluminum-transported-by-...? They routinely ship entire trucks full of the stuff from foundries to forges over public highways.

The melting point of aluminum: 660°C

The melting point of iron: 1535°C

It's also much heavier. There aren't even many suitable container materials to store it, let alone ship it safely.

They do it all the time, out of the furnace comes crude iron, which then must be moved to the steelmaking plant. It is cast into bars only at the steel plant. The carbon dissolved in crude iron lowers the melting point substantially, it's around 1200 °C, so you can actually transport it in steel vessels.

They do and the technology used is a steel tube, lined with bricks.

There are "torpedo cars", that transport around 200 tons of molten pig iron by rail. Some are insulated enough to transport iron for over 24 hours. The energy advantage is massive.

> occasionally on the roughest roads some drips of molten iron fell off the back of carts while being transported

I agree.

When I studied ancient history (and Pompeii) in school we were taught that the 'ruts' were a feature of Roman roads, not a bug. Carts were specifically designed to have axle width match these ruts, and were consistent throughout the Empire [0]. I think this is a low quality article that misconstrues a research paper as actual fact.

I am going to Pompeii in September so I'll try and have a look at these iron patches anyway.

[0] - https://en.wikipedia.org/wiki/Rut_(roads)

In terms of 'ruts', the horse drawn proto-railway dates back to Corinth half a millennium earlier:

https://en.m.wikipedia.org/wiki/Wagonway#Ancient_systems

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