2 An unexpected find
During preparation of the restoration of the present bridge, research in the records indicated that a stone bridge, mentioned for the first time in 1417, may already have been in existence around 1400. At that time, the monks from Aduard were supposed to dig the canal known as Aduarderdiep (Friso & Holstein 2010).
The earliest indication on a map dates to 1560 (the ‘van Skrooten map’). The oldest picture of the bridge dates to 1675 (the ‘Hoge Justitiekamer map’), which shows a three-arched bridge constructed on two brick foundation abutments (fig. 2). This is very different from the present bridge, which was constructed by order of the Province of Groningen in 1722. It is characterised by two land abutments and a wide span. However, the original stone bridge may have been one-arched too, as the then existing bridge was to be extended “with two arches” according to a resolution dating from 1637 (Friso & Holstein, 2010, 43f).
Figure 2 Oldest known depiction (1675) of the three-arched Steentil (source: Groninger Archieven, toegang 817, inv.nr. 1059).
For the restoration of the present bridge in 2009, the water of the Aduarderdiep was pumped away from the building trench. This enabled the inspection of the land abutments of the 1722 bridge. Members of the local historical society discovered a configuration of vertical wooden piles in the heavy clay at the bottom of the watercourse, adjacent to both brick abutments. They realised the importance of this observation and reported the find to the first author. The presence of large medieval bricks suggested a medieval origin. Yet, the use of such bricks at a distance of only 1.5 kilometres from the Aduard monastery is not surprising.
The configuration of wooden piles appeared original, and the local historical society was asked to document this apparent foundation. The measurements provided insight into the construction: the poles were grouped into two densely placed grids, adjacent to the land abutments, spanning c. 10.5 m and with a width of 4.5 m. For the 1722 bridge, these dimensions are 13.0 m and 6.5 m, respectively.
A plan of the site, with the features discussed indicated, is shown in figure 3.
A sample of one of the piles was taken by sawing off the upper end for determination of the wood and dating by dendrochronology. The trunk which was sampled measured 60 cm in diameter. The wood species appeared to be willow. Unfortunately, the number annual rings was only 45, which made the sample unsuitable for dendrochronological dating. Therefore, it was decided to date the wood by radiocarbon.