A carriage ride in ancient Pompeii would have been a bone-shaking ordeal, thanks to the sad state of many of the city’s streets. But observations from a survey of these highways indicate that Pompeiians tried to restore their roads — by pouring molten iron into ruts and potholes.

More than a century before the city’s destruction in ad 79, Pompeiian workers began paving some of the roads with stone, which was soon ravaged by traffic. Eric Poehler at the University of Massachusetts at Amherst and his colleagues surveyed some 5.5 kilometres of Pompeii’s stone streets and found more than 400 iron features, including patches, drips and splatters. The team calculates that on one particularly dilapidated thoroughfare, a road crew may have poured more than 70 litres of iron or iron-rich slurry onto a section of road carved by ruts 10–20 centimetres deep.

The authors say that the repairs show the Romans could melt iron, contrary to past thinking that Roman technology could not achieve sufficiently high temperatures to do so.