Experimentation on the deterioration and filling of pits
The experimental activity is part of the PhD project of Fabio Cavulli, obtained in 2006 at the University of Padua, Department of Archaeological Sciences. The project aimed to deal in an innovative way with a problematic and much discussed aspect of Italian Palethnology: the functional-structural characterization of ancient Neolithic settlements in northern Italy. The results of the research have afterwards been collected in several articles and in the monograph "Abitare il Neolitico. Le più antiche strutture antropiche del Neolitico in Italia Settentrionale".
One of the highly problematic aspects of the debate as to the function of the sunken features is the relationship between the season that they were originally dug and the period of time between this and their eventual filling. To investigate this problem further, a unique experimental approach was adopted. Thirteen pits were dug in different seasons of the year and refilled with a variety of materials. The excavation and the observation of fillings and profiles resulting from the experimental pits have introduced new information and suggestions for the interpretation of decay processes and refilling of such features. The field work was carried out between 2004 and 2005 in a property called Giaroni locality in San Michele all'Adige (TN), made available to the University of Padua by the Agricultural Institute of San Michele all'Adige.
The experimentation carried out aimed at elaborating certain issues regarding the profile of pits and their filling. It has often been claimed that storage-pits with sides that narrow as they near the surface, if left open for a certain length of time, assume a cylindrical or “hour-glass” (“X” shaped) profile, however these assertions quite often are not based on solid observations or experiments. Moreover, the infilling sequence often turns out to be quite similar among pits found in different sites: a semi-sterile lens just a few centimetres thick at the bottom covered by one or more organic layers which fill in most part of the pit and finally a layer with lenticular section with scarce material content, seals the pit. It is therefore possible to assume that the pits were filled in much the same way: first they were left open, then intentionally filled with one or more loads of waste and finally sealed, through natural processes, with material from the surrounding area. The experiments aimed at verifying all these hypotheses and establishing the times and, if possible, the seasons of activity involved.
The results obtained consist in a variety of pit morphologies, all derived from the same initial size and shape, linked firstly to the intensity of rainfall and then the season. In spring and summer, the bottom of the pits tends to become somewhat concave and there is a slight widening at the base of the sides; in autumn, profiles obtained experimentally are very irregular, or hour-glass shaped; the most regular forms are obtained during winter. Pits with sides gradually narrowing towards the top and hour-glass profiles may derive therefore from the natural degradation of regular cylindrical profiles, even after only a few days of exposure, when rainfall is heavy and temperatures not too rigid.
The regular morphology of many pits dating from the Early Neolithic in Northern Italy would indicate winter as the period of “exposure”, or rather the period in which the structure was either left open after its initial digging or emptied of foodstuffs, fodder or other material; the second hypothesis seems the most reasonable.
In the pit infilling, organic material is compacted and transformed very quickly and efficiently. The geometry of deposition of the layers signifies their nature: simple intentional in-fillings usually have a convex upper surface, whereas the erosion of the pit walls deposits sediment along the sides giving the layer a concave surface.
CAVULLI 2008, Abitare il Neolitico. Le più antiche strutture antropiche del Neolitico in Italia Settentrionale. Preistoria Alpina, 43/2008 - Suppl. 1.
Fig. 1 - Experimental area: contour maps of the surface (10 cm), pits and mounds (after CAVULLI 2008: 280, Fig. 6.67).
Fig. 2 - 3-D model of the experimental area, different views (after CAVULLI 2008: 280, Fig. 6.68).