Lidar is a laser survey, usually flown from an aircraft, that measures the height of the ground in fine detail. Archaeologists use it to spot faint banks, ditches and sunken lines of Roman roads, even under trees where photographs show nothing.
Key takeaways
- Lidar measures the ground surface with laser pulses, and the results can be turned into high-resolution elevation models.
- It can reveal low features hidden by vegetation, which suits roads that survive only as a faint bank or hollow.
- A lidar find supports a road line, but it does not date the road or prove it is Roman.
- Only 2.7% of our road length is classed certain, so lidar and other fieldwork still have much to confirm.
How lidar works for roads
Lidar (light detection and ranging) measures distance by timing laser pulses. Flown from an aircraft, it records the height of the ground in fine detail, and the result can be turned into a high-resolution digital elevation model [1]. In archaeology it is used for planning fieldwork, for mapping features under forest canopy, and for seeing broad, continuous features that are hard to pick out from the ground [1].
That suits Roman roads. Many survive only as a low embankment, a shallow ditch or a worn hollow. On the ground, undergrowth can hide them. Lidar can reveal micro-topography that vegetation hides [1], so the shape of the land shows up much more clearly. A long straight line crossing field boundaries and following a route that would have connected two Roman places is a good candidate for a road.
Lidar is one method among several. It sits alongside cropmarks seen in aerial photographs, geophysical survey and excavation. See how to find Roman roads for the others.
An example from our data
The Itiner-e team identified roads from archaeological excavations and surveys and located them by digitising existing maps and studies, correcting against satellite imagery and terrain [2]. Our data does not say which lines were helped by lidar, and it records no remote-sensing detail at all.
What the data does show is how much remains uncertain. Only 8,181 km of road, 2.7% of the network, is certain. In the United Kingdom the UK page still shows 98.8% conjectured. Dere Street is 273 km long, and 100% of it is conjectured in this data. Such lines are the places where new survey could most improve the picture.
The thing people get wrong
Lidar is often described as if it could scan the countryside and show a finished map of buried Roman roads. In practice it gives a surface model that people must interpret. A bank seen in lidar may be a Roman road, but it might also be a medieval track, a field boundary or a later drainage line. It is usually followed by fieldwork to check. And because it only sees what survives at the surface, it cannot show roads that were completely levelled or are deeply buried, which is where cropmarks or geophysics may help instead.
Frequently asked questions
Can lidar find features under woodland?
It is used to map features under forest canopy, and it can produce models of the ground that are otherwise hidden by vegetation.
Does lidar prove a road is Roman?
No. It shows a shape in the ground. Dating a road needs excavation, finds or other evidence.
Is lidar used in your map data?
Not directly. The Itiner-e lines come from published studies, maps and satellite imagery, though some of those studies may themselves rely on lidar.
Sources
- Lidar, Wikipedia.
- Itiner-e: A high-resolution dataset of roads of the Roman Empire, Scientific Data (Brughmans et al., 2025).
- Cropmark, 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).