5 Conclusion
The precisely dated age range of the willow pile firmly establishes the felling period of the tree between 1285 and 1295 AD. The pile was part of a vertical construction driven into the heavy clay to support the land abutments of a brick stone bridge crossing the Aduarderdiep. As written sources suggest, the Aduarderdiep has been dug around 1408 (Mol & Delvigne 2010, 166ff); consequently the first mentioned stone bridge crossing the Aduarderdiep cannot predate the digging. However, our result shows that the bridge is older. This leaves open two possibilities. One, the 1285-1295 bridge crossed a natural predecessor of the present Aduarderdiep, a branch of the Peizerdiep system, and the canal was dug at a later date using the ancient stream bed. Two, the Aduarderdiep is at least a hundred years older and was already in existence around 1285-1295. We consider the second possibility more likely, for two reasons. First, at the location of the Steentil an ancient course of the Peizerdiep has not been observed. The nearest stream deposits are located a few hundred metres to the east. Second, the builders constructed a foundation ‘in the monastic way’, i.e. using wooden piles, like they did for the Aduard monastery previously. If the old Peizerdiep was still in its natural state by then, a simple ford would also suffice to cross this watercourse.
We assume that the first Steentil bridge was constructed by order of the Cistercian monks, who introduced the engineering of raising brick structures on weak subsoils. The excavation of the Aduarderdiep was conceived to improve the freshwater discharge of the hinterland and the water transport of goods and persons. The construction of a bridge added the opportunity of regulating both road and water traffic. The relatively wide span of 10.5 m between the bridge abutments enabled an easy passage of freight vessels, and it is likely that their passage was in some way controlled by the Aduard monastery.
At present, the Steentil is the oldest stone bridge observed in the monastic landscape of the northern coastal region of the Netherlands. Yet an even older bridge support, made of oak, was found in the Westerwolde district of Groningen. This wooden construction bridged a man-made stream and dates back to the early 12th century, when monasteries were not yet present in the northern region and brick was not available.[2] The discussion concerning the influence of the monasteries on the semi-cultivated landscape of the northern Netherlands, as it existed at the end of the High Middle Ages, has only just begun (for Aduard: Mol & Delvigne 2010). The presumption of a drastic change gains ground, as the scale of interference is more and more understood as a result of correlated measures, taken by the monasteries, foremost the Cistercians. This comprises the improvement of waterways, the cutting of peat and the embankment of the expanding tidal inlets. However, exact data on monastic interventions, other than written evidence, are rare. The Steentil find sheds light on both water and road management at the end of the 13th century.
The comprehensive report on the Steentil restoration project (Friso & Holstein, 2010) is not clear concerning the meaning of the single wooden pile dated. We are however convinced that the wood sampled, measured by radiometry and yielding a very precise historic date range, takes away all doubts concerning the age of the wood. Theoretically, the piles could originate from an older structure, being recycled, but this is contradicted by the presence of bark. We have no knowledge about the lengths and possible traces of earlier use. We consider earlier use not very likely. The trunks could only survive below the ground water level, as willow is very sensitive to rot. Moreover, the extraction of such piles from a wet soil like peat or clay seems hardly feasible. Therefore we conclude that the piles discovered in 2010 under the Steentil belong to an original construction dating from the late-13th century.
All piles, including the one sampled, were left in the soil and once more have disappeared under the water surface.
Henny Groenendijk
h.groenendijk@provinciegroningen.nl
Groningen Institute of Archaeology, Groningen University, the Netherlands
Hans van der Plicht
Center for Isotope Research, Goningen University, the Netherlands
Harm Jan Streurman
Center for Isotope Research, Goningen University, Groningen, the Netherlands
Review data:
Submission: 15/3/2011
Revised submission: 22/3/2012