Archaeological excavations have finally answered the question regarding the age and development of the mysterious prehistoric fields enclosed by earthen ridges known as ‘Celtic fields’.

Using Optically Stimulated Luminescence (OSL), a technique that dates the last exposure to light or heat sources of quartz minerals, archaeologist Stijn Arnoldussen from the University of Groningen managed to determine that these banks around the later prehistoric field plots were constructed more than 3100 years ago and remained in use for hundreds of years thereafter. Until now, no reliable dates were available to securely date the Dutch Celtic fields. Moreover, his research indicated that the Celtic field-banks were constructed out of sods taken from wet heathlands, near alder carrs or from stream valleys. Such sods were taken to the settlements, mixed with dung and domestic refuse and – akin to modern fertilizer – taken back to the field plots as manure. Through the process of uprooting field weeds and then discarding them at the field’s edges, this mixture came to form banks, ever so gradually, between fields. Over the course of hundreds of years, c. 1 m high banks developed.

Research

Through manually digging small test-pits and analysing hundreds of soils samples from the banks and Celtic field plots at Lunteren (municipality of Ede, the Netherlands), Arnoldussen successfully managed to determine how the banks were constructed and to accurately date the banks. These excavations were conducted in cooperation with the Municipality of Ede, the Province of Gelderland and land-owner ‘Stichting Geldersch Landschap & Kastelen´. “The problem is that we have known the locations of these Celtic fields for decades thanks to aerial photography and, more recently, due to laser altimetry analyses”, states Arnoldussen, “but that we essentially were clueless about how the banks were constructed or for what period of time this system of embanked fields was in function”. This is peculiar, as Arnoldussen argues that “Celtic fields are one of the most extensive and still visible types of archaeology in the present-day Dutch landscape”. Indeed, the size of Celtic field systems can be vast. The Celtic field complex targeted by the Groningen Institute of Archaeology at Lunteren measured at least 210 hectares in prehistory.

Age of the Celtic field banks

Through the application of a special technique that dates the last heat- or light-exposure of quartz particles (Optically Stimulated Luminescence dating or OSL, in collaboration with the Netherlands Centre for Luminescene dating at Wageningen University), various soil samples from the Celtic field banks could be dated. “The results are way more spectacular than anticipated!”, exclaims Arnoldussen, “It showed that the Celtic field system remained in use for hundreds of years: certainly 700 years, but possibly even for one millennium!”. The prehistoric banks were constructed around 1100 cal BC but were still increasing in height 700 years later. It is probable that their use spanned into the Roman era. This shows that Celtic field systems are not only vast in surface area, but also represent an agricultural landscape of unprecedented stability and durability. “This most have been an utmost traditional agricultural system”, clarifies Arnoldussen, “in which is was of vital importance to continue the planting, tending to and harvesting of crops in the same ways, and on the near same spots, as your ancestors”. Palaeobotanical analyses of the samples showed that barley, wheat and flax were cultivated. According to Arnoldussen, there has never been a (agri)cultural landscape in the history or the prehistory of the Dutch, that surpasses the Celtic field system in permanence and durability.

Celtic field banks

The composition of the Celtic field banks was previously subject to debate, states Arnoldussen: ”Many wild theories have been brought to the fore, for example that the banks consisted of cleared-out tree stubs, stones or driftsand, yet none of these were found during our excavations of the banks. The banks rather appear to comprise mineral and organic sods of low-lying, wet, parts of the landscape that were mixed with dung and debris at small prehistoric hamlets.” As the excavation of the Groningen team was situated on the high-and-dry flank of a Saale-period glacial ridge (the Goudsberg of Lunteren), the team was initially somewhat puzzled by the discovery of plants of wet landscapes (lesser bulrush, sedges, alder pollen) on the ridge. “They would have needed to walk two kilometres to lower lying land beyond the glacial ridge in prehistory”, clarifies Arnoldussen, “but as we have also found charcoal indicative of alder trees used for firewood from the same lowland areas, they presumably used ox-powered carts to do the heavy lifting.”

Despite these important discoveries, the investigators are adamant that there is still much to be learned. “We now know the age of several banks in two Dutch Celtic fields, yet the precise ways in which the Celtic field agriculture was executed (crop rotation, fallow period, and interspersed occupation) and whether Celtic fields in other parts of the Low Countries are similar, remains unclear”, according to Arnoldussen. Therefore, this summer, Arnoldussen sets out to excavate yet another Dutch Celtic field, this time within the coversand landscapes of the Southern Netherlands.

A full publication of the research discussed is published on the open access repository at the University of Groningen.