Roman roads look straight because surveyors lined them up between high points that could be seen from each other, then built the road as direct as the ground allowed. They still bent for steep hills, rivers and marshes.
Key takeaways
- Surveyors sighted along rods between points that could be seen from each other, so long runs came out dead straight.
- Straight roads were quicker to travel and used less material than winding ones.
- Roads bent where hills, rivers, marshes or crossing points forced them to, so many are straight in sections rather than from end to end.
- The Fosse Way, Ermine Street and Stane Street are all famous for straight sections, and our map shows each one as 372 km, 421 km and 93.3 km long.
How the straight lines were set out
Engineers first inspected the ground and roughly fixed a route. Surveyors then marked the line with rods and a groma, sighting along the rods to keep it straight. A signal fire could mark a distant end point [1]. In practice this meant picking high or prominent points, aligning the road between them, and filling in the stretches that could not be seen directly.
Straight lines suited the Romans. They shortened journeys for soldiers and messengers, and a direct road needed less material and less repair than a winding one [1]. In Britain the key sites were linked by the most direct routes possible [2].
Where roads bend
The Romans often preferred to engineer through obstacles, cutting through hills rather than going round them [1]. But straight did not mean ruler-straight from end to end. Roads changed direction where there was a steep slope, a river crossing, a marsh or a settlement they had to reach. A long road is usually a chain of straight lengths joined at turning points. Very steep straight roads were also often impractical for carts, and the Romans sometimes built longer, easier alternatives [1].
An example from our data
Three English roads show the pattern. The Fosse Way is 372 km long in our data, Ermine Street is 421 km and Stane Street is 93.3 km. Each is known for long straight runs, and you can see the long runs on the map by zooming in. This site does not measure straightness, so we give no figure for it. Be careful when judging straightness from the map. Most of these lines are conjectured, with 99.1% of the Fosse Way in that class, so the map's line is itself an estimate, and a drawn estimate tends to look smoother than the real route.
The thing people get wrong
The idea that Roman roads never bend is a myth. Straight sections are common, especially on newly built military roads, but roads were routed around real obstacles and some follow older tracks. When a modern road kinks, that does not prove it is not Roman, and a straight line on a map does not prove it is.
Frequently asked questions
Were Roman roads perfectly straight?
No. Many sections are very straight, but roads changed direction for hills, rivers and other obstacles.
Is the line on the map exactly where the road ran?
Not exactly. Only 2.7% of the network length is classed as certain, so most lines are best estimates.
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).