What do the layers in the main harbour of Birka tell us?
Gästblogg av Felix Rösch, en av de marinarkeologer som deltar i årets undersökning på Birka. Felix forskar om Schleswigs tidigmedeltida hamn och har tidigare bland annat deltagit i undersökningarna av Hedebys hamnområde. Han deltog även 2012 i undersökningarna av Birkas hamn.
As an archaeologist who focuses on viking age and medieval harbours it was a matter of course to return to Birka also in 2013. Last year’s excavations have been very generative and helped us to learn more about harbour structures in a Viking age metropolis like Birka. While the 2012 years excavation mainly aimed at the stone settings and their possible role as remains of jetties, the current campaign tries to find out more about the pile settings in front the harbour as well as the stratigraphy of the sea ground.
The excavation site for 2013 with the jetty and the dive plattform.
The stratigraphy help us to get an idea about when Birka and its main harbour were into use and at what spots the most actions have been taken out. Therefore a trench of 2 x 3 m has been set up to be excavated as well as some systematical drilling in order to get core samples has been taken out. The first results are really instructive. The Viking age and thereby Birka’s existence is clearly visible in the layers. On the top of the natural grown glacial clay, there is a thick layer packed with men made organic material consisting mainly of wood chips.
Kulturlagret bestående av huggspån och träflis och med en knävel (tvärslå) liggande ovanpå.
Those kinds of layers archaeologists call culture layers. During Birka’s existence hundreds of craftsmen worked close to the shore and dumped their remains in the water. The light organic material floated around awhile in the harbour until it sank down to the sea ground. There it mixed with clay and got stuck. As far as it can be judged by now the culture layers is to be divided in three parts. The lower and upper parts consist of clay with some organic remains, while the middle part virtually only exists out of those organics. So this part reflects the time span when Birka was heavily frequented and one of the major places in the Baltic. Datings based on natural sciences as well as several types of findings deliver hints when the harbour was in use and what type of crafting took place. After Birka was abandoned, the culture layer has been naturally covered with silt so it has been preserved until nowadays. Great luck for us archaeologists and those who are interested in the Viking age.