When the Romans did something, they usually went big — and their military campaigns are no exception. It took them 200 years to conquer Spain, but they did it so methodically that traces of that campaign can still be detected. Now, researchers have used remote sensing instruments to detect 66 Roman army camps, showing a larger military presence than previously thought.

At its peak, the Roman empire sprawled across Europe, Northern Africa, and even parts of Asia, ranging from today’s Iran to Southern Scotland. Much of their success was owed to their culture and ability to manage the logistics of such a large territory, but the Romans would have never become the superpower they were without their military prowess. The Romans loved to wage war, and they were good at it.

Soldiers often spent years on end campaigning in foreign lands, covering huge distances in the process. The Roman military was nothing if not organized, and they paid great attention to how they set military camps, making it so that the camps offered protection from both the elements and potential foes. If you were to come across a Roman army camp back in the day, you’d know it was a Roman camp.

Luckily for archaeologists, some of the telltale signs of this camp organization are still visible today, though not at ground level.

To catch a glimpse of these ancient camps, researchers used satellite images, aerial photography, and airborne LiDAR — a method using an airborne laser to create 3D representations for the ground, ‘seeing’ beneath the vegetation. Things like ditches and ramparts may not be visible to the naked eye, but there’s still a trace of them left in the subsurface, and this can be detected. Some are visible on Google Earth, while others require this sort of remote sensing tool.

The team would start by looking for known Roman campsites and the probable routes that Romans would have taken, and looked for signs of camps on Google Earth: crop marks, most of the time. The ditches and fences the Romans built may not be there anymore, but the soil keeps a record of them in its chemistry and porosity. A soil that was dug by the Romans could, for instance, have a different humidity than the surrounding soil, even 2000 years later. Armed with this knowledge, the team would then set on to ground proof their finding and through fieldwork and different sets of aerial imagery, find out more about the presumed Roman camp.

Using this approach, the researchers have discovered 66 Roman camps, mostly located at the foothills of the Cantabrian Mountains, where much of the fighting took place at the end of the 1st century BC. This suggests that Roman soldiers navigated the environment to their advantage, switching between lowlands and uplands and using ridges in the mountains to avoid detection and gain strategic ground.

Dr. João Fonte from the University of Exeter, one of the study authors, said:

“We have identified so many sites because we used different types of remote sensing. Airborne laser scanning gave good results for some sites in more remote places because it showed earthworks really well. Aerial photography worked better in lowland areas for the detection of cropmarks.”

“The remains are of the temporary camps that the Roman army set up when moving through hostile territory or when carrying out manoeuveres around their permanent bases. They reveal the intense Roman activity at the entrance to the Cantabrian Mountains during the last phase of the Roman conquest of Hispania.”

Even now, there are only so many places you can set camps in the area. Most of these Roman campsites later became important Roman towns. Sasamón, a village in Burgos is probably very close to where Emperor Augusto established his camp during his presence in the front.

The discovery of camps of different sizes even allow researchers to understand how the Romans attacked the indigenous population from different angles, learning more about the Roman presence in the Iberian peninsula.

The work is still ongoing, and you can check out more of the team’s discoveries at RomanArmy.eu — it’s in Spanish, but the browser translator does a pretty good job.

You can also read the entire study here.