To the east of Birdoswald is a lake called Crag Lough. From here archaeologists have extracted soil samples to show how this landscape changed when the Roman troops pulled out. This process, known as pollen analysis, involves examining the types of trees that once grew here.

Crag Lough, Birdoswald
Crag Lough

I like trees, which is why I’ve planted them on my farm. But to archaeologists, trees on land that had once been farmed show that the countryside has been abandoned. And in the dark age that traditional view is that the countryside reverted to a wild wood once the Romans had withdrawn.


The work at Crag Lough near Birdoswald challenges this view. It was carried out by Dr Petra Dark of Reading University.

Birdoswald Research

Dr Petra Dark “Pollen analysis gives great evidence for what the countryside of the past was like. We can actually identify the pollen grains of different plants, like the trees, the cereals and so on. We can count the pollen samples taken in cores of sediment and reconstruct vegetation change over long time-scales.”

Petra is able to build up a picture of what the landscape looked like centuries ago.

Petra Dark “Cereal pollen tells us they are growing crops nearby. Tree pollen tells us there was woodland nearby, and this is very important for reconstructing changes in farming, because we can see where they were farming intensively, or had land abandoned to farming, in which case would quite rapidly revert to woodland.”

Pollen Charts
Pollen Charts

By carbon-dating the samples, Petra is able to tell when a landscape changed.

Petra Dark “By the Roman period, this is quite an open landscape, a lot of woodland is gone.”

Petra’s charts clearly show that at Hadrian’s Wall, there was not a huge increase in forest when the Romans pulled out.

Dr Petra Dark Scientist

Petra Dark “By the end of the Roman period, we start to get an increase of birch pollen. but the other trees are not really changing, so that isn’t a massive woodland regeneration happening.”

Dr Petra Dark
Dr Petra Dark

Contrary to popular belief, the landscape at Hadrian’s Wall did not revert to forest when the Romans left.

Petra has compared samples from a number of sites across Britain. While some do see an increase in woodland, at many the land continued to be farmed in exactly the same way, and in certain places land use intensified after the Romans departed.

Petra Dark “We can’t generalise across the whole of the landscape in the way they did in the 1950s, before we had this evidence. That’s much too simple a picture.”

Petra’s work demolishes the vision of Britain reverting to wild wood once the Romans departed. In forts like Birdoswald and towns like Wroxeter, the end of Roman administration did not cause the breakdown of society.

Released from the controlling hand of Rome, new leaders emerged and society regrouped. But this new independence did not mean Britain had cut herself off from the rest of the world. A series of extraordinary contacts were about to be made with some of the most powerful players in the ancient world.

Birdoswald and the famous Crag Lough