It’s hard to imagine the landscape of the Netherlands without its dykes. But just how old are these typically Dutch earthworks? This is what Prof. Jakob Wallinga, Chair of Soil Geography and Landscape at Wageningen University & Research, will be investigating in the EARTHWORK project. Along with quite a number of external partners, he hopes to gain a better understanding of how and when our predecessors modified the landscape to improve their living conditions.
“Earthworks are monuments with which people have modified the landscape. They include dykes, dwelling mounds (terpen) and banks. They also include plaggen soils, which are elevated areas resulting from fields being fertilised over a long period of time. The soil was raised a little year by year,” explains Wallinga. “Earthworks are highly visible in the landscape and are made of natural material, such as sand or clay. But we often don’t know when these earthworks originated. We’d like to find out more about that.”
Dykes are an excellent example of earthworks. We can’t imagine our small country without them. “It’s interesting to look at their history: when were these dykes constructed? Building them requires some coordination; it’s not something you can do on your own,” says Wallinga. “You also need large quantities of turf sods, clay and sand from the surrounding area.”
But how do you date the earthworks? Nico Willemse from RAAP (an independent research and consultancy company for archaeology, cultural history and heritage and one of the partners in this research) explains how this normally works. “Archaeologists have different ways of dating layers and features in the soil – for example, on the basis of finds, such as pottery sherds or coins. But you don’t usually find those items in a dyke. Another method is radiocarbon dating, for which you need wood or other organic remains. We don’t usually find them in dykes either.”
Analysing grains of sand
In the EARTHWORK project, researchers are therefore using a different technique to date the earthworks. It’s called luminescence dating and Wallinga is the expert in this field in the Netherlands. He explains: “We determine when grains of sand were last exposed to light. We take samples from various depths in the dyke, making sure that no light gets in. We then take the samples to our laboratory, which is like a darkroom, but instead of developing photos, we analyse grains of sand. For each grain we investigate when it last saw light.
You have a mix of grains in a dyke: some were exposed to light when the dyke was built, while others weren’t. These would have been exposed at an earlier time. Grains can also become mixed up after an earthwork is built, for example as a result of the digging activity of worms. For each grain, we therefore measure when it was last exposed to light. This gives us an age distribution. We then use clever statistical methods to work out from this distribution when the earthwork was constructed.”
The study examines six types of earthwork. In the low parts of the Netherlands, these are dykes and dwelling mounds (also called woerden/wierden in Dutch). In the higher parts of the Netherlands, the researchers will focus on plaggen soils, banks and prehistoric ‘Celtic’ fields. Wallinga: “Another interesting object that we’re investigating is the Roman aqueduct near Nijmegen. That really appeals to the imagination. Attempts have previously been made to date it, but there were fewer opportunities then to conduct the analysis at the level of grains. In this project we hope to take the next step.”
Wageningen University & Research is collaborating with many different partners in the research project. Willemse explains: “We’re all helping each other in the research. Take RAAP, for example: we do a lot of soil research. If we’re investigating objects of interest, we can involve WUR. At the same time, we can use Wageningen’s knowledge in the fields of luminescence technology and landscape archaeology. That's how we learn from each other.” Several municipalities are also involved in the research. Willemse: “These municipalities are aware of the value of the earthworks and are keen to see research done on them.”
A unique feature of the project is the involvement of museums such as GeoFort, De Bastei and Museonder. Wallinga: “Archaeology really captures people’s imaginations. We want to share the results of our research with the wider public. And these partners can help us with that. By sharing the stories, the earthworks will come to life. People will start looking at their own environment in a different way.”
Impact on the present
With the research, WUR is connecting the past with the present. That’s because the earthworks that were constructed hundreds of years ago are still having an impact on the landscape of today. Wallinga again uses dykes as an example: “Normally, the land floods and the river deposits sand and clay. If you erect a dyke, the land behind it no longer floods, which means you can live there. But it also means that no new soil layers are deposited and that the land subsides when the soil compacts.”
Impact on the future
Today too, we are faced with challenges posed by the environment. Take climate change and sea level rise. Wallinga: “Like our predecessors, we will have to make modifications to the landscape to ensure that we human beings can continue to live here. We can be inspired by what people have done in the past. But we have to be very conscious about any adaptations we make. And we have to be aware that the changes we make to the landscape now are irreversible. Our actions today determine the landscape of the future. The EARTHWORK project connects the past, present and future. Isn’t that amazing?”
Wageningen University & Research has received a grant for the EARTHWORK project as part of the NWO programme ‘Future directions in Dutch archaeological research’. Prof. Jakob Wallinga’s research application was judged as ‘outstanding’. WUR will appoint two PhD candidates for the research study.