A Pre-Roman Iron Age Settlement at Børglumvej, Århus: Archaeology and Environment

Abstract

A Pre-Roman Iron Age Settlement at Børglumvej, Arhus: Archaeology and Environment

In 1991 a small Pre-Roman Iron Age settlement was excavated in advance of construction work at Børglumvej, north of Århus. The settlement lay on a low ridge, and close by there was a marshy hollow which had contained a small lake in Iron Age times. Remains of the settlement were excavated and a section was cut through the lake deposits revealing a culture layer contemporary with the site. The archaeological investigations showed that the settlement had only had a limited period of use. This fact, in conjunction with the organic sediments preserved in the hollow, made the locality particularly suited to a combined archaeological/environmental investigation.

Archaeology

The settlement comprised a longhouse (Hus I) and an outbuilding (Hus II/III) plus a number of pits of varying size (fig. 1). There were no remains of an enclosing fence but the settlement is estimated to have occupied an area of C. 15 X 30 111.

Finds from the site were dominated by pottery (see fig. 2), but also included iron slag and a granite saddle quern.

The deposits from the former lake occupy a small hollow measuring c. 35 x 35 m, which lies c. 30 m to the west of the settlement (fig. 1). A sketch diagram of a section through the deposits is given in fig. 3. Finds were restricted to the culture layer (lag 4) and comprised mostly pottery which closely resembled that found at the settlement. Other finds included some animal bones, a hammer stone and some waste flakes of flint. The culture layer was thickest at the lake margin closest to the settlement.

Dating

The house remains showed only limited evidence of rebuilding and it appears that the settlement had a short lifetime -a maximum of two phases, perhaps 50 years. The long­house (Hus I) is of a type common in Jutland in the late Pre-Roman and early Roman Iron Ages. The pottery from the settlement and the lake deposits is so similar that it must be contemporary. It is typical of Period IIIa of the Pre-Roman Iron Age which extends from c. 200 BC up to the decades just preceding the birth of Christ.

Environmental investigations

During the excavation of the settlement samples were collected for plant macrofossil analysis from postholes and pits. Samples for both pollen and plant macrofossil analysis were also taken from the section through the lake deposits. The aim was to investigate the economy and environment of the settlement and the history of the organic deposits in the hollow.

Plant remains from the settlement.

A total of 21 soil samples were taken from the settlement (table 1), 13 from postholes in the longhouse (Hus I), 5 from postholes in the outbuilding (Hus II/III) and 3 from a large pit CD (fig. 1). The samples were processed by flotation, after which the carbonised plant remains were sorted and identified in the microscope.

The plant remains in the soil samples were poorly preserved and present at low concentrations (table 2). A total of27.5 carbonised cereal grains could be identified from all the contexts. Of these 15.5 were of naked barley (Hordeum vulgare var. nudurn), 4 were of bread wheat (Triticum aestivum) 2 were possibly emmer (T. dicoccum) and there was one grain each of unspecified barley, wheat and possibly oats. The weed seeds were dominated by arable weeds and ruderals. A single carbonised tuber of Ahrrenatherum elatius ssp. tuberosus was also recovered. This plant is known as an arable weed but has also been used as a food plant in the past. Heathland and wetland plants were also represented.

Analysis of deposits in the former lake

A sketch diagram of the stratigraphy of the section through the lake deposits showing the locations of samples taken for pollen and plant macrofossil analysis is given in fig. 3.

Pollen analysis and chronology

A total of 11 pollen analyses were carried out. The samples were prepared using standard procedures and the results are given in table 3.

The pollen concentration at 234 cm and 224 cm was low and many grains were very corroded. The composition (Betula with same Pinus, several species of Salix, Artemisia, Cyperaceae, Selaginella and several other light­demanding herbs) shows that the basal layers in the lake (layers 7-10) were formed during a relatively warm period in the Late Glacial, presumably the Bølling and/or Allerød Periods.

At 164 cm the pollen content was characterized by Gramineae, Cyperaceae, Artemisia and Empetrum, showing that layer 6 was formed under relatively cold conditions, presumable in the Younger Dryas.

Two samples were examined from layer 5, one from the lower part (150 cm) and one from the upper (134 cm). In each case tree pollen made up 50% of the pollen content, but otherwise the two samples were quite different. The pollen content at 150 cm (Betula, Pinus, Populus, Juniperus, Salix, Gramineae, Cyperaceae, Gymnocarpium dryopteris) shows that this level dates from the Pre­Boreal. At 134 cm many more tree species were represented and Gramineae and Cyperaceae pollen was abundant. The large amounts of Ulmus pollen and absence of anthropogenic indicators date this level to the Boreal or Atlantic Periods. Together these two analyses show that layer 5 was either formed slowly over an extended period or that there is a hiatus in the stratigraphy which is not obvious in the section.

The boundary between layers 5 and 4 (the culture layer) is very irregular. The lower 10 cm of layer 4 was dominated by tree pollen, including abundant Corylus, Pinus and Tilia. Avena and Hordeum pollen was present together with that of a number of anthrapogenic indicators. This spectrum probably dates from the Bronze Age, showing that a considerable period elapsed between the formation of the deposits at 134 cm on one side of the boundary and 129 cm on the other i.e. the layer boundary is an obvious hiatus.

In contrast, the pollen spectra in the remainder of layer 4 had a low tree pollen content, and species such as Plantago lanceolata, Gramineae, Taraxacum-type and Cyperaceae dominate. Pollen of Secale, Triticum and Avena was also present along with large grass pollen grains of which at least same were probably of Hordeum. The spectrum is consistent with a dating around the birth of Christ which is in accordance with the archaeological dating of the settlement.

Two pollen samples were analyzed from layer 3, at 97 cm and 90 cm. Tree pollen had only low values in these samples which are in turn dominated by the pollen of anthrapogenic species. Hordeum-type pollen was abundant along with the other cereal species and annual arable weeds such as Rumex acetosella, Chenopodium type, Scleranthus annuus, Centaurea cyanus. Fagus pollen was relatively common in the lower part of layer 3, where there was also a little Secale pollen. This suggests that the deposits date from Roman Iron Age or later. Centaurea cyanus was only found in the upper part of the layer, where Secale pollen was considerably more common than in the lower part. Centaurea cyanus is known primarily from the Middle Ages but has also been found in alder deposits. There is therefore same uncertainty whether the upper part of layer 3 comes from the late Iron Age or early Middle Ages. No analyses were carried out on the uppermost layer which is thought to comprise recent fill.

Plant macrofossils in the lake deposits

Three samples were analysed from the lake deposits, two from the culture layer 4 -one from near the margin (prøve 1), the other from the centre of the hollow (prøve 2)- and one from the centre of layer 3, which is interpreted as washed-in plough soil (prøve 3)). The samples were wet-sieved before being analysed. All three samples, and in particular sample (prøve) 3, comprised very fragmented and decomposed plant material and contained relatively few identifiable plant remains.

The plant remains in layer 4 give nevertheless a detailed picture of the vegetation in the lake during the Iron Age; shallow open water in the centre of the lake with Lemna sp, Batrachium sp, Chara sp, Glyceria fluitans and Potamogeton sp and lush vegetation at the margin with Alisma plantago-aquatica, Sparganium sp, Juncus sp, Carex and other Cyperaceae as well as Menyanthes trifoliata, Thalictrum, Cicuta virosa, Scirpus sp and Mentha sp.

Terrestrial planes were also represented but in view of the close proximity of the settlement, the concentration of remains of crops, arable weeds and ruderals was very modest. It is possible that the dense vegetation around the margin screened the lake from windblown plant remains.

The presence of oospores of Chara and caddis fly larval cases shows that the water in the lake was relatively unpolluted as these two organisms cannot survive if the phosphate level of the water is too high (Chara) or the oxygen content two low (caddis fly larvae). It seems likely therefore that the culture layer was not a refuse layer but a layer formed naturally but under human influence. The small refuse component in layer 4 can perhaps be explained in terms of material thrown in by for example children. No well was found associated with the settlement and it seems likely that the lake was used as a source of water.

Layer 3, which is interpreted as being largely comprised of washed-in plough soil, contained very few identifiable plant remains. Seeds of Lemna and achenes of Batrachium show however that there was still open water in the hollow when the layer was formed. It is not possible to deduce anything about the vegetation of the lake margin at this time as the only identifiable plant in the layer were a few embryos of Alisma plantago-aquatica.

Conclusion

Pollen analysis has shown that the lake deposits in the hollow are incomplete, in that a greater part of the Mesolithic and Neolithic is not represented. Neither was it possible to follow the post-Iron Age history of the hollow as the upper layers were unsuited to pollen or macrofossil analysis. Despite these limitations the site proved to be very well-suited to an investigation of the environment and culture activity around the lake in the period from the Bronze Age up into the first centuries AD. The results of the pollen and plant macrofossil analysis complement each other well, giving us a very detailed picture of events at this time. Evidence about the surrounding landscape comes mostly from the pollen analyses whereas macrofossil analysis has given the most information about the vegetation in and around the lake.

In the Bronze Age the area was characterized by woodland, which included Tilia and Corylus, interspaced with open grazed areas and arable fields. Myriophyllum verticillatum and Potamogeton grew in the lake and Alisma plantago-aquatica, Sparganium and a variety of ferns grew around the lake margin.

Towards the end of the Pre-Roman Iron Age the settlement was established and the landscape at this time was very open and very much dominated by agriculture. The carbonized plant remains from the settlement complex reveal the diversity of the arable agriculture associated with the settlement; naked barley, bread wheat, hulled barley and possibly also emmer and oats were cultivated. Pollen analysis suggests that rye may also have been present and this picture corresponds well with the results of the few other investigations from this period. Carbonised weed seeds were relatively abundant in postholes and the refuse pit but it is impossible to determine if these had been used as a food source as has been found to be the case at other sites.

Potamogeton and Sparganium still grew in the lake at this time, together with plants such as Chara, Lemna and Batrachium. The lake margin was occupied by Alisma plantago­aquatica, Juncus, Mentha, Cicuta virosa, Menyanthes trifoliata and a number of other wetland plants. The remains of Chara and larval cases of caddis flies show that the water was relatively unpolluted despite clear evidence for animal bones, stones and pottery having been thrown out into it. The amount of refuse material in the layer is not great however in view of the settlement probably having been occupied for a period of 50 years. No well was found in association with the settlement and it seems likely that the lake was the main source of water. It is also possible that the lush vegetation along the lake margin screened the lake from windblown plant remains.

After the settlement went out of use the landscape maintained its open character and it appears that arable fields came to lie close to the lake such that plough soil was washed out into it. The rich lake shore vegetation which was present during the occupation of the settlement apparently vanished and this may have contributed to transport of material into the lake which accordingly became progressively shallower.

Bent Aaby, David Robinson & Anne Bloch Jørgensen