Tag Archives: Roads

The passage of Roman carts eventually led to ruts in the road, as seen above. Credit: Eric Poehler.

Ancient Romans used molten iron to repair their stone-paved roads

The passage of Roman carts eventually led to ruts in the road, as seen above. Credit: Eric Poehler.

The passage of Roman carts eventually led to ruts in the road, as seen above. Credit: Eric Poehler.

The devastating eruption of Mt. Vesuvius in 79 AD destroyed the city of Pompeii, killing thousands. But the deadly hot ash and lava also helped to preserve the ancient city and the remains of its inhabitants. In a new study, archeologists uncovered a previously unknown method of Roman street repair, which involved pouring molten iron over deep ruts in the road.

Potholes: an ancient problem

For centuries, one of Rome’s greatest advantages over its enemies was its huge and intricate network of stone-paved roads. From the Firth of Forth in Scotland to inland North Africa remains of these iconic landmarks have survived to this day — and in some cases even formed the basis for certain modern roads today.

All Roman roads were built by the Roman military, which employed various specialists for this occasion. According to Paternus, a Roman senator in the 3rd century AD, the first thing that legionaries would do when they were tasked with building a Roman road on behalf of the new governor or the procurator would be to use ‘agrimensores’. These were land surveyors who did all the surveying using measuring equipment to lay out the route of the road. Then, ‘liberators’ or land levelers would level the land that the road was going to be built on, followed by ‘Mensores’, or quantity measurers who would then measure out all the various quantities of the various stages of building the Roman road.

Roman road works were really sophisticated, and their maintenance was no different, as we’ve learned from a new study published in the American Journal of Archaeology. During a 2014 survey of Pompeii’s streets, researchers at the University of Massachusetts Amherst and the University of Texas at Austin were surprised when they consistently found iron between and below paving stones of the city’s most important streets.

“Recent research on the costs of paving stone streets in terms of time, money, and opportunity provides the economic context for this novel repair process and shows the use of iron and iron slag to have been an expedient alternative,” the authors wrote in their study.

Like other major towns, most of Pompeii’s streets were paved with stone. However, the passage of carts on a daily basis eroded the stones, forming deep holes and ruts which are still easily visible to this day. In fact, over a century and a half ago, the American satirist Mark Twain based his complaints about the corruption of city officials at Pompeii on these cavities:

“Have I not seen with my own eyes how for two hundred years at least the pavements were not repaired! – how ruts five and even ten inches deep were worn into the thick flagstones by the chariot-wheels of generations of swindled tax-payers? … I wish I knew the name of the last one that held office in Pompeii so that I could give him a blast. I speak with feeling on this subject, because I caught my foot in one of those ruts, and the sadness that came over me when I saw the first poor skeleton, with ashes and lava sticking to it, was tempered by the reflection that may be that party was the Street Commissioner,” he wrote.

Although the Romans were quite advanced in their public works (and corruption was indeed a problem in Roman society), Twain was perhaps not aware of how complicated road repair during that time could be. Repaving the street was out of the question in most situations — it was simply too expensive and time-consuming. If a narrow street was damaged, traffic could be blocked for months until specialists finished repaving the street.

Examples of iron fillings and drops on Pomepii's ancient stone-paved streets. Credit: Eric Poehler.

Examples of iron fillings and drops on Pomepii’s ancient stone-paved streets. Credit: Eric Poehler.

In Pompeii, at least, the Romans devised a creative solution to their problem. The city’s engineers heated iron to a molten state, then poured the material onto, into, and below the eroded paving stones. Hundreds of individual street repairs were discovered thus far in the city.

The molten iron was poured alongside other filler materials such as stone, grounded terracotta, and ceramics. Once the metal cooled down, the whole mash solidified to completely fill and cover holes. According to the archaeologists, this method was much cheaper and quicker than repaving a street.

It’s not exactly clear how the Romans carried out such repairs, but the researchers have some clues. We know that the iron would have needed to heat to about 1,600ºC (2,912ºF), a temperature which Roman furnaces could accommodate. Iron drops were found on sections of the street that didn’t require repair, suggesting that it was accidentally spilled while being carried, a task likely reserved for slaves.

In the future, the researchers hope to analyze the chemical composition of the iron from the street filings to find its source. They would also like to survey more Pompeii streets.

Simulate your way out of (or into) the perfect traffic jam

Traffic jams are a universally miserable experience, no matter when or when they happen. There are numerous factors that can cause one to happen. Sometimes, when the cause is clear, say construction works or a car crash that needs to be cleared away, most of us can keep our frustration in check. But when you’ve been spending the last half hour inching your way to an intersection and then passing through without seeing any apparent reason for the slowdown, it’s much, much worse. The pointlessness of it all is enough to bring you to your boiling point.


But there’s always a cause behind the jam, even if not readily apparent. Computer models like Traffic-Simulation are designed to figure out how each traffic component adds towards this infuriating result. The simulation models various conditions such as the number of trucks or cars on the road, average distance and speed of cars, lane geometry and so forth, to explain how traffic jams develop. The idea is to use the simulations to figure out what might happen if traffic patterns shift, and predict problem areas before they happen.

The website was created by Dresden University of Technology Professor Martin Treiber, and can currently model a single scenario, but more features are planned for the future. The ring road was implemented first to illustrate ‘shockwave’ slowdowns — traffic jams that progress through a line of traffic from the first row of cars, as described in this video from the University of Nagoya, Japan:

So even in perfect conditions, with everyone driving at the same speeds, it’s still really hard for everything to run smoothly (except if you’re an ant). Even something as innocuous as adjusting the number of trucks on the road can cause unbelievable congestion in the simulation. So give it a go, try toying around with the variables to find what it takes to make traffic flow merrily along or create the mother of all traffic congestions.

And next time you’re stuck in traffic you’ll have a much better understanding of exactly “why. aren’t. we. moving. forward?!” Not sure that’s going to make the experience any more pleasant, though.