arvistro" said:
I wonder though if Polish quarter estimate is about Modern Poland territory (read Prussians!) or the grey area in picture.
Prussians I think had high death rates.
Teutonic Order's Realm in Prussia was also - like Poland & Milan - relatively lightly affected by the Black Death plague in year 1349.
Later in 1373, 1382, 1416, 1427 and 1439 other plagues took place, but they mostly affected cities (while ethnic Prussians lived mostly in villages). So the Black Death didn't have a major impact on reducing the % of Prussians among the population of Prussia.
And the impact of those later plagues on cities wasn't really that deadly, compared to what Western Europe had suffered.
In 1404 there took place a census of Prussian farmsteads in lands of the Order (but apart from lands of the Order there were also lands owned by bishops and lands owned by private owners in the Teutonic Order's Realm - so the census was not complete).
Based on that census ethnic Prussians can be estimated as ca. 55-60% of the population of original Prussia in 1404. The rest were mostly Germans plus some Poles and others. Of course the Teutonic Order's Realm was already larger than ethnic Prussia at that time, as since 1309 it included Pomerelia (which was later labelled West Prussia, but that was ethnically Slavic land - Balts didn't live there).
In 1404 ethnic structure of Prussia (original one - so areas which were later known as East Prussia) was such, that cities were mostly German-inhabited, while the countryside was mostly Prussian - but in westernmost parts of the country (just to the east of the Vistula River) ratio of Prussians to Germans in villages was like 3 to 5, in northern part of Ermland bishopric Prussians were roughly 50% of villagers, in southern part of Ermland bishopric (the area which was later Polonized) they were 75%, in Natangia 90% and in Sambia 100%.
So the % of Prussians in the countryside was a west-east continuum - from some 35-40% in western regions, to 100% in Sambia.
Unsurprisingly, Sambia was the area where Prussian language survived for the longest time (until early 1700s).
All in all, if we also add Prussians living in towns and cities, they were some 50%-60% of the population of [East] Prussia in 1404.
And that was mostly the result of losses during the 1200s and high immigration of foreigners, rather than the Black Death.
Prussians also had the lowest status of all ethnic groups in Prussia - lower than German and Polish settlers. About 2/3 of Prussians were unfree serfs, the remaining half were mostly peasants - there existed also quite numerous Prussian nobility (even though Prussian nobles suffered especially high losses during the crusade of the 1200s), but they were the ones most likely to adopt German culture and identity, so that Prussian masses were deprived of native high culture and reduced to living under German domination.
All Prussian clans who broke the Treaty of Sirgune of 1249, were reduced to serfdom after the conquest (1283). That applied also to nobles, punished for opposing the Knights. While traitors who collaborated with the Order against other Prussians, were rewarded.
The assimilation of the lowest social stratum of Old Prussians into foreign cultures took place only after the Teutonic Order collapsed, and the Lutheran Duchy of Prussia emerged. The Teutonic Knights even had such a saying:
"let the Prussians remain Prussians", but don't get deluded - the Knights weren't into multi-kulti, that saying was about low legal and social status, not about culture.
Systematic discrimination of Prussians and "Prusianness" by the Knights led to assimilation of higher strata of the Prussian society. Prussian language became gradually limited just to serfs (2/3 of all Prussians). Ironically - the end of that discrimination (which took place after Prussia transformed into a secular Lutheran Duchy) - led to assimilation of those serfs as well. Immigration of at first Germans (13th - 14th c.) and then Poles and Lithuanians (15th - 16th c.) also contributed to the melting of Prussians into other ethnicities.
For example the Prussian tribe of the Warmians - which consisted of "clan districts" Wewa, Plut, Medenowe, Wuntenowe, Lanzania and Drusen - adopted mostly Polish ethnicity (language and culture), rather than German. They also remained Catholic after the Reformation, because Warmia was incorporated to Poland in 1466 and was also administered by bishops. By contrast Ducal Prussia became a secular and Lutheran country.
Another factor which contributed to assimilation of Prussians was migration of peasants from villages to towns. Towns in East Prussia were established by the Teutonic Order and were initially mostly inhabited by Germans. But over time (after year 1400) the influx of German settlers became small, while more of Prussians and other ethnic groups began to migrate to towns in East Prussia. That was not a sudden occurence but a gradual process, so Prussians who came to towns were adopting German language rather than imposing their Baltic language on the locals.
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Ethnic Prussians were up to 60% in Prussia in 1404, which is not bad, considering that they had been conquered and colonized.
Today ethnic Swedes are probably just 70% of the population in Sweden, even though nobody has conquered and colonized them.