A medieval ditch and a new great mound!

In 2013 we placed the first trench on what we today call the Eastern plateau. Our initial hypothesis was that we were dealing with yet another house plateau from the Vendel or Viking period. A mound for long been registered on the hill/plateau and it was presumed to be later. There are couple of other cases in Sweden where a mound has sealed and earlier building.

When we started the excavation in 2013, it quickly became confusing. We found a stone filled ditch that resembled the wall foundations of the great hall and houses on the northern plateau. But there was no clear floor layers or finds from the Late Iron Age. When the 14C-dates arrived, they showed that the ditch, the only clearly house indicating feature, was dated to the 12th and 13th c. AD. That means that it is contemporary with the Romanesque cathedral.

Another strange feature was a huge cairn beneath the sandy layers. This discovery awakened a lively discussion. We threw ourselves between different explanations. Were we dealing with the cairn of a damaged mound or had the house plateau a central cairn, quite different from the other plateaus in Gamla Uppsala, but with parallells from other sites in the Mälar region such as Fornsigtuna. It was very hard to find a final conclusion which was the primary reason for this years excavations on the plateau.

When we started this year it was possible to reach a far larger part of the plateau because that Statens Fastighetsverk, the land owner, had removed a large old thicket of lilac in an excellent way. We quickly found that the stone filled ditch stretched all along the plateau. It probably represents the earliest border of the 12th c. church area. It is thus a forerunner of the Late medieval stone wall which was rebuilt around 1812 but still have the old outline.

We got one final answer to our questions when we made a cut into the mound in order to finalize the stratigraphic relation between the mound and the plateau. After going through a very interesting sequence of mound layers that require a separate story, a cairn was reached. It is definitely the same cairn we found in 2013. We are simply dealing with the core of a very large mound  that have been damaged and encapsulated in the 12th c. probably about the same time as the cathedral was built. Some of the mound fill has been taken away and additional sand and gravel has been piled up in order to create a plateau for the enclosure of the church area. On basis of datings of layers that now can be related to the mound, it seems to be dated to the 7th c. That means that it do not deviate a lot from the other great mounds (Ljungkvist 2008). Preliminary measurements indicate that it is at least 30 m wide but damaged. It is thus probably the fifth largest mound found in Gamla Uppsala. Its central cairn seem to measure more than 25 meters. In Peter Bratts (2008) thesis of excavated mound in Middle Sweden, the largest measured cairn is 20 m wide. That mound is the East Mound in Gamla Uppsala, the immediate neighbor our mound.

Parts of the grave cairn that in 2013 was found just below 12th c. sand layers. These were first interpreted as parts of a house plateau. The mound fill has been completely dug away in the 12th c. which made it very difficult to understand the stratigraphy. The medieval architects were probably satisfied with removing the mound soil and the cairn was a perfect solid foundation for the plateau.

Our cut into the mound. Below a large sand layer on the top and a lower complicated series of thin coal, soot, silt and sand layers, the cairn appears. It is now clear that a substantial part of the plateau rests on the grave cairn. Much of the mound layers are gone. Why they chose to let some parts of the mound stick up from the plateau surface is a delicate topic for the future.