The origin of these types of buildings can be traced to Pomeranian culture of the the late bronze age and early iron age, which developed from Lusatian culture. One of the best examples of the Pomeranian wooden architecture is the fortified town of Biskupin. Biskupin was an Iron Age fortified settlement in north-central (Wielkopolska) Poland (Kuyavian-Pomeranian Voivodeship). When first discovered it was thought to be early evidence of Slavic settlement but archaeologists later confirmed it belonged to the Biskupin group of the Lusatian culture.
There are two settlement periods at Biskupin, which was located in the middle of a lake but is now situated on a peninsula, that follow each other without hiatus. Both settlements were laid out on a rectangular grid with eleven streets that are three meters wide. The older settlement from early Iron Age was established on a slightly wet island of over 2 hectares and consisted of ca. 100 oak and pine log-houses that are of similar layout and measure ca. 8 x 10 m each.They consisted of two chambers and an open entrance-area.These houses were designed to accommodate 10 to 12 persons. An open hearth was located in the centre of the biggest room. There are no larger houses that could indicate social stratification. Because of the damp, boggy ground the streets were covered with wooden planks. This is the reconstruction of one of the log cabins from Biskupin that can be seen in the Biskupin open air museum.
The settlement was surrounded by a tall wooden wall, or palisade, set on a rampart made up of both wood and earth. The rampart was constructed of oak trunks that form boxes filled with earth. The rampart is more than 450 m long and accompanied by a wooden breakwater in the lake. 6000–8000 m³ of wood have been used in the construction of the rampart.
The settlement at Biskupin belongs to the Hallstatt C and D periods (early Iron Age, 800-650 BC and 650-475 BC). However, dendrochronological analysis provided more accurate dating. It proved that oak wood used in the construction of the settlement was cut down between 747-722 B.C. Over half of the wood used was cut during the winter of 738/737 B.C.
What is very interesting is that the tradition of building dwellings and fortifications from logs was during the early Iron age found only in Pomeranian culture south of Baltic sea and not in Jutland or in Scandinavia.
The tradition of building log cabins was continued by the Central European Celts. This is a reconstruction of a Celtic house in Havranok, Slovakia.
The Havránok hill fort was an important religious, economic, and political center of the Púchov culture (300 BCE - 180 CE), in which the dominant Celtic tribe of Cotini mingled with the older people of the Lusatian (Pomeranian) culture.
In the early medieval period we find that the tradition of building dwellings and fortifications from logs was still exclusively found among Slavs living in the same area of the old Pomeranian Culture, south of Baltic sea, and further east, but not in Jutland and not in Scandinavia. As a matter of fact, the similarity between the Iron age Pomeranian log dwellings and fortifications, and Medieaval Slavic Pomeranian log dwellings and fortifications is so striking, that when Biskupin was originally discovered, it was presumed that it was a Medieval Slavic fort. Only carbon dating showed that Biskupin was in fact 1000 years older.
Here is an example of a typical Medieval Slavic fort: Chotěbuz - Podobora:
Slavs built both square semi-subterranean (sunk in) dwellings with heating devices in a corner and ground dwellings. They also used both log only and log frame with wattle doub construction technique.
Here are the reconstructions of completely sunken and semi sunken Medieval Slavic hut from Slovakia based on the actual discovered huts remains dated to the 6th - 7th century AD:
And this is what these types of houses looked like inside. Please note a built stone oven in the corner:
And here is a reconstruction of a Medieval Slavic surface log cabin, based on archaeological finds from Staré Město ("Old Town"), a town in the Zlín Region of the Czech Republic, again dated to the 6th - 7th century AD.
The same building technique using logs was unknown in Scandinavia until the 11th century, the time of the closest cooperation and intermixing between the Norse and the Slavs. This all indicates that log cabins and fortifications are a Slavic cultural import into Scandinavia.
When looking at the introduction of the joint timber houses in the Germanic areas of the Baltic, we have to look at the Jutland and other Danish areas of the southern Scandinavia separately from the Northern areas of Scandinavia. These two areas were politically and culturally separate and were linked to different Slavic tribal group. The Danes were politically and culturally linked with the Western Slavs (Polabians, Obodrites, Serbs, Poles) and the Norse and Swedes were politically and culturally linked with the Eastern Slavs (Rus). There is no wander then that in these two areas of Scandinavia we find two different types of the joint timber construction techniques.
In the Danish controlled areas, the earliest constructions of lying and crossing logs were found in the fortification rampart of Danevirke in southern Jutland, built in the 8th and 9th centuries. A similar technique has been found in a few houses in Haithabu (Hedeby) near Danevirke in the 9th century and in a well in Kaupang in Norway in the beginning of the 9th century. The type of wood used was oak which was cut lengthwise to get appropriate dimensions. The logs had a rectangular section, and the joints had both an upper and a lower notch that were rectangular. In Wollin and Gdansk (Poland), there were also joint timber houses made of oak wood, mostly built of round logs, but occasionally also of rectangular ones. The woodworking skills needed to build these houses were so advanced that they must have been developed somewhere else and then brought to Jutland. This points to the technological import from the South Baltic Western Slavic territories (today Germany and Poland) where joint timber houses were also constructed from oak wood for millenniums. The same types of rectangular oak profiled log houses were also built by Serbs in the Balkans and are still built today.
Here is an example of the advanced joint timber houses from Serbia. You can see that the oak logs were longitudinally split into beams (thick planks) which are then joined together using deep rectangular joins.
This is another house from Serbia which shows even more complicated rectangular log construction technique. This technique combines the wooden frame made out of thick square profile oak logs and thinner horizontal wooden beams (thick planks). The wooden beams with external joins are inserted into the internal joins on the vertical holding beams.
In the work entitled: "About the Introduction of Joint Timber Building in Scandinavia", Karin Rosberg from Uppsala university argues this is exactly what happened.
In the intro to the paper Karin says that the issue of the introduction of joint timber building is old in both Norway and Sweden. Former Swedish researchers, such as Boëthius, Erixon, and Lundberg, have been very uncertain about this, and Lundberg believed it was introduced as early as during the Vendel Period, i. e. 550-800 AD. A few decades later, Hauglid in Norway assumed, with some caution, that it was introduced by king Harald Hårdråde in the middle of the 11th century.
She then proceeds to explain where and when the earliest joint timber houses and other structures were built, after which she describes similarities and differences between the Slavic and Scandinavian joint timber techniques for building houses. Finally this is what the author of this work thinks about the reason why the Scandinavians adopted joint timber building so late (1000 AD), even though they were for centuries in contact with Slavs who built the joint timber houses and fortifications?
"As I said before, joint timber building has very good heat qualities, which is needed in the Scandinavian climate. Accordingly, one would expect the Scandinavians to be quick to adopt a solid building technique which would also save much work with wood cutting for heating. And they did so at last, and the heat qualities were certainly an essential reason for joint timber building dominating in Scandinavia for about 900 years. But they did not adopt it until such a long time had passed as 200 years. Why? I suggest the reason for the delay was cultural. The Scandinavians readily adopted foreign dress fashion and consumer goods, but not so readily foreign housing. They probably had much of their identity in the houses, especially in their dwellings. The house shows who is the owner, and for the Vikings an old family was important. So a traditional Viking long house could be associated with an old and impressing family. In addition, for the Vikings their house was a sacred place and had a religious dimension. Such things made the housing more conservative than other cultural features. There are theories, expressed by Rapoport, about socio-cultural factors having a considerable impact on house form, and about house form having a considerable degree of constancy due to culturally linked aspects. These theories point in the same direction as my suggestion. Towards the end of the 10th century, the cultural difference between the Scandinavian and Slavic peoples decreased. (My comment: This happened due to a long period of political cooperation and cultural and physical mixing (intermarrying) between the Scandinavians and the Slavs. This eventually lead to the large Slavic settlement in Scandinavia and equally large Scandinavian settlement in the Slavic countries). Eventually they both—or at least parts of them—converted to Christianity. All this probably made the Scandinavians more ready to adopt the Slavic joint timber house building tradition. "
But once the Scandinavians did start making log cabins, they made them their own, to the point when today everyone thinks that joint timber log cabins are a native Scandinavian tradition. So much so that today even Slavs believe that they borrowed the technology for building their own joint timber log cabins from Scandinavians. Funny how things like this happen.
The below picture shows a typical joint timber log cabin from Scandinavia (Stockholm). Please note that it uses the same horizontal beam joining constriction technique like the first hose from Serbia that I showed above.