1 Introduction
Earlier descriptions of Celtic fields in the Netherlands range from Heydensche legerplaatsen en wallen (pagan settlements and walls; 17th c.), Roman camps (18th c.) to camps in general (19th c.). The interpretation as arable land was given by Van Giffen (1928) following English publications introducing the name Celtic fields. As early as 1911 these landscape structures had been described for Denmark by Sophus Müller and interpreted by him as arable fields. Hatt (1931) called the system Oldtidsagre (old arable fields) and gave an explanation for the formation of the banks by the accumulation of debris from the fields. Van Giffen (1944 a.o.) thought that the banks were gradually formed by the removal of the exhausted and thus infertile topsoil. Modderman (1955) strongly opposed this with the argument that it would mean removing the best part of the soil.[1] So did Jankuhn (1956-57): after taking away the humic upper layer and so exposing the infertile sand underneath, arable cultivation would have been made impossible.
According to Brongers (1976, Ch. V) the banks were formed by clearing the fields of stones and tree stumps. He also brought forward stratigraphical arguments for the transport of material from the fields on to the banks, and a mathematical model showing that in a later stage humic material must have been brought in from outside, to improve soil fertility.
Spek et al. (2003) concluded that the banks were deliberately raised at the field boundaries during the last stage of cultivation (Middle Iron Age, Early Roman period), by bringing in material both from inside the banks (the fields) as well as from outside. In the last stage (Late Iron Age to Roman period) cultivation would have taken place on the banks.
It seems that there was ample space for such practice: the width of the earthen banks measures between 3-16 m: Examples are: Øster Lem Hede, Denmark, 3-6 m (Helt Nielsen [2009]), Noordse Veld, Zeijen, 6-12 m, and Vaassen, c. 8 m in the Netherlands (Spek et al. 2003), Brongers 1976) and Flögeln Haselhörn, Germany, up to 16 m (Zimmermann 1976).