A Plank Tank from Nantwich

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A Plank Tank from Nantwich. Robina McNeil and A.F. Roberts write: In July 1985 Mr and Mrs Piggin of St Anne's Lane, Nantwich were digging foundations for a bungalow (SJ 648523) and uncovered a wooden structure. They collected the finds and contacted Archaeological Services, Liverpool University. On examination the structure was found to be a plank-built tank, or box, which was sunk into a tailor-made pit. The tank consisted of two courses of edge-set planks. Of the lower course the four interlocking radials, split slightly wedge-shaped, had identical dimensions (I.58m x o.32m x o.o4-o.o8 m), with a tenon at either end on one edge only. The planks interlocked with one tenon resting on the shoulder of the next plank, to form a square tank with internal measurements of i.44m (4ft 9ins). This method of construction needs no pegs or nails to tie the members together. The varying width of the planks meant that in some instances the tenon protruded for up to o.o4m beyond the outside edge of the tank. A square tapering stake and a large wooden chock were rammed against the exterior to prevent the sides of the container from collapsing outwards. This type of jointing is favoured in the construction of square or rectangular boxes, as for instance the Saxon well at Portchester Castle67 and Well IV at Colchester,6 which have similar bracing timbers, and was developed periodically in conjunction with saddle joints, in the top tiers of the Skeldergate Well, York.69 The higher planks rested directly on the base wall planks. The west plank and presumably its eastern counterpart had a tenon under which the north and south planks were held in positions. These upper planks appear to have been set in front of the base wall planks. This position is probably the result of slumping and the correct position is either directly above the lower planks or set behind them. The wood of the superstructure was less well preserved than the lower planks, so, although the timbers appear ill-fitting, they may originally have been more substantial and designed to repeat the jointing of the lower timbers. The tank has no floor. Immediately above the natural sand was a dense organic mat which has been identified as cess. The majority of the finds were found by the landowner whilst digging out the foundations. They came as far as it was possible to ascertain from the deposits immediately above the tank. A few more sherds were found later in the spoil heap. No finds were recovered from the tank or from its surrounding pit; except for two or three sherds of post-medieval pottery, the pottery was of Roman date and is discussed below.