Camber is the slight curve across the top of a road, higher in the middle and lower at the sides, so rain runs off into ditches. Many Roman roads were built with a camber to keep the surface drained and last longer.
Key takeaways
- Camber means the road is highest in the middle and slopes gently to each side.
- It sheds rain into the side ditches, which protects the surface and the foundation.
- Camber is one part of a drainage design that also used raised banks and ditches.
- Our map shows route lines only: even for the 352 km Watling Street, it records no surface detail.
How camber works
Camber is the gentle arch across a road. The middle sits higher than the edges, so rain runs sideways off the surface instead of pooling on it. Roman roads were cambered and flanked by footpaths, bridleways and drainage ditches, and the surface was crowned, or arched, for drainage [1]. The aim was a road that resisted rain, frost and flooding and needed as little repair as possible [1].
Camber works with other parts of the design. In Britain a road often sat on a raised bank, the agger, which lifted it above wet ground, and shallow ditches took the water away [2]. Together these kept water out of the stone foundation, which is where roads fail.
The arch was gentle. How much camber a road had depended on its width, materials and local ground, and the amount seen on an excavated road today is also shaped by wear and later repair.
Camber on paved and gravel roads
On a gravel road the camber was part of the shape of the metalling, the compacted stone and gravel on top. On a paved road the paving stones themselves were laid to form the arch [1]. Either way the principle was the same: let the water go to the sides. Edge stones and side strips for pedestrians and animals framed the carriageway, with ditches beyond [1]. Because the camber depended on the surface layer, it was among the first features to disappear when a road was robbed of its stone or ploughed, which is one reason excavated roads often look flatter or lower than the original.
An example from our data
The map cannot show camber. Watling Street is 352 km long in our data, in 58 segments, and it has 16 Roman places matched along it. For the Watling Street, as for every road in Itiner-e, the dataset records route, certainty and type, not surface shape. Excavations have found that Watling Street was wide, around 10.1 m in one recorded measurement [2], but that is a feature of a particular excavated stretch, not a figure for the whole road.
The thing people get wrong
Many people expect a Roman road to be a smooth, flat surface. Where paving survives, the material between the stones has worn away, so old paved surfaces look bumpy. The original surface was much flatter [1]. Another common idea is that camber was a special Roman invention. The Romans used it widely, and the same idea is still used in road design today.
Frequently asked questions
Why did Roman roads have a camber?
To drain water. Standing water and frost damage roads, so shedding rain quickly helps them last.
Are Roman roads still cambered?
Modern roads use the same idea, and some worn Roman surfaces keep traces of it, but weathering and repair have changed most.
Sources
- Roman roads, Wikipedia.
- Roman roads in Britannia, Wikipedia.
- Every figure from our own map is worked out from the datasets on the data sources page (checked against Itiner-e version 2024 1.3).