Situated in the northern part of the Jura Mountains, the Delémont valley is a closed basin circumscribed by two mountain ranges, peaking at an altitude of about 1000 m and cut by several gorges. Located on the floodplain of a modest tributary of the Sorne river to the southwest of the town of Delémont (Canton Jura, Switzerland), the site "En La Pran" lies at a mean altitude of 426 m.

The Section d'archéologie et paléontologie of the Office de la culture conducted several campaigns of test trenching in this sector, prior to the construction of a feeder and a maintenance centre of the A16 Transjurane motorway. The excavation of the site, begun in some urgency, lasted without interruption from January 1996 to May 1999 ; a final campaign took place between June 2001 and March 2002. The extensive use of a hydraulic excavator for excavation allowed us to uncover and document a total surface of 4 ha covering archaeological remains menaced by destruction.

The oldest traces of human presence uncovered at Delémont - En La Pran date to the Late Mesolithic and Early Neolithic periods. After a break of nearly four thousand years, the site was reoccupied, as remains dating from the end of the Middle Bronze Age and the beginning of the Late Bronze Age demonstrate. The Late Bronze Age occupation included an urnfield cemetery and traces of several buildings, revealed mainly by linear find concentrations. Structures and finds dating from the subsequent Iron Age, the roman and the medieval periods indicate a more or less continuous occupation or use of the site and are all contained within the main archaeological layer, a palaeosol formed during the Bronze Age.

The 346 features discovered on the site were grouped according to their morphology (chap. 2) ; a majority consists of excavated features (pits, postholes, ditches and graves containing cremated remains), but surface concentrations of finds or waste were also documented. A rough chronological classification allowed us to draw two schematic plans locating all the features dating respectively to the Bronze and to the Iron Age. The detailed analysis of these remains will be published in three subsequent volumes of this series (CAJ 23, 24 and 25).

The second part of the volume concentrates on the environment. First, an analysis of site stratigraphy and sedimentology allows us to characterise the various layers that form the small flood plain of the stream " La Pran " (chap. 3). The identified sediments belong mostly to fluvial deposits, separated by palaeosols or organic layers. The typical sequence is formed of five sedimentary units. The archaeological layer belongs to unit 3 and laterally connects to palaeochannels containing finds dating to the Bronze and Iron Ages: it dates to the second part of the Holocene. The site was divided into six sedimentological domains, each having a different depositional history. In domain D, also known as " ancient meander ", important information on the evolution of the environment between 3100 and 1200 BC was acquired. In this domain, organic materials are particularly well preserved, encouraging us to engage in a pluridisciplinary approach.

The analysis of plant and seed remains highlights the changing nature of the environment, evolving from the bottom to the top of the sedimentary sequence (chap. 4). Around 3100 BC, a mixed deciduous forest covers the valley. Beginning in the Early Bronze Age, the forest gradually retreats and species indicating open spaces and riverside forests appear. Cultivated plants become increasingly important, indicating increasing forest clearance and agriculture from the Middle Bronze Age onwards.

The analysis of plant pollen reveals a similar pattern (chap. 5). Layers dating to the Early and Late Atlantic contain no clear traces of human impact. The first indicators of deforestation appear only during the Subboreal, starting with the Early Bronze Age and reaching a peak during the Late Bronze Age. Fragments of wood preserved in the waterlogged lower layers were also analysed (chap. 6). Fir dominates clearly, although its natural habitat does not include the floodplains situated at the bottom of alluvial valleys. It is therefore likely that the wood was transported from the surrounding slopes, the likely location of a fir forest. The analysis of mollusc shells provides additional information on the environment (chap. 7). It confirms the presence of a humid broadleaf forest next to the stream, apparently subject to local natural or manmade disturbance. This riparian forest grew denser with time and the mollusc fauna indicates the presence of marshy areas.

In the following chapter (chap. 8), the results of the various environmental studies are synthesized and integrated into a chronological diagram. This general schematic covers the period between 2000 and 200 BC. Three drawings reconstructing the past environments allow us to visualise the flora and the course of the stream as they were respectively in the Middle Bronze Age, the Late Bronze Age and the Iron Age.

The third and last part of the volume contains a description of the finds dating to the periods preceding the Late Bronze Age.

In chapter 9, the flints found mostly concentrated in a horizon dating to the Late/ Final Mesolithic and the Neolithic periods are analysed. Refitting, stratigraphic position and spatial analysis indicate that a majority of these finds were discovered in situ. Eight flint concentrations could be located. The typological classification of the tools and the technological analysis of the debitage revealed major differences between the flints found in concentration 1 and those belonging to the concentrations 2 to 8. The presence of a round-bottomed pot, associated with a flint assemblage characterised by triangular points, transverse arrowheads, a trapeze and a spindle-shaped point, date concentration 1 to a late phase of the Early Neolithic, around 4800 BC. The sites of the Hinkelstein culture found in the Rhine basin provide the closest parallels, indicating that the neolithisation of the Delémont valley probably occurred from the north-west. The assemblages of the concentrations 2 to 8 all date to the Late/ Final Mesolithic, but it has not been possible to determine whether they represent a single spatially discontinuous occupation or a series of repeat visits by one or several groups of hunter-gatherers.

The Bronze Age finds predating the Late Bronze Age occupation are presented in chapter 10. Most belong to an assemblage of potsherds discovered in a palaeochannel located mainly within the sedimentological domain B. The typo-chronological classification of the pottery starts with the description of the material, grouped according to its provenance from several successive stratified layers (chap. 10.2). The characteristic pieces are then compared with known Middle Bronze Age and Late Bronze Age sites. The stratigraphically separated assemblages appear to be chronologically somewhat mixed, but the pottery clearly indicates that the site was occupied from the end of the Middle Bronze Age onwards. The discovery of particularly well-preserved pottery at the very bottom of the sequence is somewhat surprising ; are they remains of a votive deposit ?

The final chapter contains a reflexion on the predictive value of test trenching, the preservation of archaeological remains in an open environment and the adaptation of excavation methods to different circumstances (chap. 11). In conclusion, the multidisciplinary approaches presented in this volume permit us to put forward a new model of the settlement of the Delémont valley and the canton of Jura between the Mesolithic and the Bronze Age.

Translation: Robert Fellner