Four archaeological sites situated to the south of the village of Alle (Les Aiges, Pré au Prince 1 and 2, Sur Noir Bois) and a fifth located to the west of the small town of Porrentruy (L'Etang) were excavated between 1990 and 2001, prior to the construction of the A16 motorway in the canton Jura, Switzerland. The documented surfaces are relatively small (between 120 and 2800 m2).

The discoveries made south of Alle document the evolution of rural settlements from the Late Iron Age to the roman period. During the latter part of the La Tène period, a series of isolated farmsteads (Pré au Prince 1 and 2, Sur Noir Bois, Les Aiges) replace the Early La Tène hamlet of Alle, Noir Bois. Their location changes through time. Due to the limited extent of the excavations, our understanding of the internal organisation of these farms remains incomplete.

Together, the Late Iron Age sites discovered in the Jura provide an image of the settlement of this region, which appears quite similar to the contemporary occupation of the Swiss plateau and northern France. The plains, covered by an open vegetation, are quite densely occupied by isolated farmsteads. These are sometimes enclosed by a ditch and are often found in small hollows or at the edge of the floodplain. With the exception of the single documented hamlet, Noir Bois, each settlement consists of a small number of rectangular post-built structures, varying in size from 6 to 65 m2. Some of these can be clearly indentified as houses, others represent small granaries with a raised floor. None of the structures are particularly luxurious and the finds are mostly of local origin. A distinctive feature of the local settlements seems to be a marked preference for the cultivation of millet and the raising of caprids.

Agriculture apart, the usual domestic activities were practiced (flour grinding, textile spinning and weaving). Traces of pottery production and ironworking were also found.
Several sites were occupied without interruption form the late La Tène to the gallo-roman period. However, only Les Aiges appears to have remained active until the middle of the 4th century AD.
The excavation of this site revealed only a part of the pars rustica of a villa. Here, three granaries succeeded each other over a considerable period; observations made in the field allow us to recognise four principal phases. Numerous cereal grains from the last three phases illustrate the evolution of the local agricultural production.

Phase 1 (50 BC - 50/75 AD) is represented by a post-built structure of 48 m2, interpreted on typological grounds as a granary (building 1). During phase 2 (50/75 - 180/200 AD), this early building is replaced by a much larger granary, measuring 282 m2. This timber structure was built on stone foundations and roofed with tiles (building 2). The plan of the building was later extended by an annexe of 110 m2. To the south, postholes of various sizes indicate the presence of other constructions, probably a residential area.

After the destruction of building 2 during a fire, phase 3 (180/200 - 250/275 AD) sees the construction of an even larger granary (544 m2), this time with stone walls (building 3). Grain was stored on a raised floor supported by joists. Slightly later, two annexes were added to the southern façade and increased the surface to 710 m2.

Phase 4 (250/275 - 350 AD) sees the reconstruction of building 3 after a second fire. It continues to serve as a granary. A new feature is added: narrow stone walls support the raised floor, providing a ventilation space. The latter part of phase 4 sees a radical change in the function of the building, it is no longer used as a granary. It seems likely that he pars urbana was destroyed, displacing the residential area into areas previously reserved for economic use. New wooden buildings appear to the south and the west of the former granary, probably providing residential space for the agricultural work force. A small granary was constructed on sill beams to the north.

Over 56000 botanical remains were found at Les Aiges, allowing us to reconstruct the evolution of local grain agriculture. As in other La Tène period settlements of the Jura, millet is dominant during phase 1. From the middle of the 1st century AD, barley becomes the main cultivar. Gradually, it becomes less dominant, diminishing from 86 % of cultivated grains in phase 2 to only 27% in phase 4. Oat also gradually decreases ; conversely, bread and spelt wheat gain continuously in importance.

The study of the faunal remains also illustrates changes in animal husbandry. During phases 2 and 3, caprids are most common, followed by cattle and pig. During phase 4, cattle predominate, followed by pig. Possibly, changes in husbandry are linked to the evolution of grain agriculture. The faunal remains also included several falcon bones (phase 4). They represent one of the rare relics of falconry in 4th century Western Europe.

The site of Porrentruy, L'Etang, consists of a pavement bordering a swampy area, made up of construction debris and numerous finds. Apparently, these remains originated in a settlement located upslope of the humid depression, but which was completely destroyed by erosion.

Translation: Robert Fellner