The Borussians or Prussians (the latter term being derived from the first) were a Baltic people living on the south-eastern rim of the Baltic Sea, between the Vistula and the Niemen.
After the conquest of the Prussians by the knight-monks of the Teutonic order (13th century) and the foundation of the Duchy of Prussia (1525), the term Prussians was finally used to designate all the inhabitants of the duchy (then the kingdom) , who were predominantly of German origin.
The so-called Old Prussian language died out in the 17th century.
The Borusses ("the almost Russians") would have individualized, within the sub-group of the Western Balts, from the fifth century. Subsequently, they split into several tribes. The Aesti mentioned in Germania by Tacitus may well have been Prussians. Tacitus compares them to the Suevi, a group of Germanic peoples, but having a language resembling Celtic languages.
The Borussians were originally divided into nine clans with which the Galindians, Sudovians and Skalvians were associated more or less permanently. Thus, the chronicles sometimes mention twelve provinces of pre-Teutonic Prussia. The Nadruvians were the most powerful clan and the one which subsequently resisted the Germanic invasion and assimilation the longest.
Disappearance of the Baltic Prussians in favor of the Germanic Prussians
After attempts in 997 and 1114 to subdue the Western Balts, the Duchy of Mazovia intensified its attacks, from 1209, to subdue these pagan peoples. In retaliation, they made incursions into Mazovia. Unable to defeat them, Duke Conrad I of Mazovia first invited the Knights of the Teutonic Order to settle in his territories, on the border with the Borussians, then encouraged them in 1231 to enter the territories of these latter. With the Golden Bull of Rimini, Emperor Frederick II and then the Pope proclaimed Prussia the march of the Empire, as such entrusted to the guard of the Teutonic Knights. In the middle of the 13th century, the Borussians attempted a final revolt which only precipitated their decline. The Prussians of the southwest were defeated and conquered in ten years; those in the south-east and north-east were conquered in the second half of the 13th century. In the year 1300, all the western Baltic peoples were under the authority of the monastic state of the Teutonic Knights. From 170,000 around the year 1200, the Borussians were no more than 90,000 around 1300. Prussia then became a land of German colonization: agricultural land was generously given to settlers from German-speaking regions, originating from northern Germany. , Friesland and Holland.
Subsequently, there were two big waves of new arrivals in Prussia:
in the 16th century, following the adoption of Lutheranism in Prussia and the wars of religion in Germany;
At the end of the 17th century, the Revocation of the Edict of Nantes in 1683 expelled the Protestants from France, and their departure for the countries of Refuge was mainly oriented towards Prussia at the invitation of Brandenburg. In 1709-1710 the region was ravaged by the plague and, to repopulate certain deserted regions, many Germanic Protestant populations were called upon from the region of Salzburg and German-speaking Switzerland.
The arrival of migrants began a marked decline in the use of Old Prussian and the native populations gradually adopted the language of the newcomers, which was also that of the administration. The Old Prussians, few in number because already largely decimated by the Teutonic Knights in the 13th century, suffered a policy of Germanization which resulted in their assimilating to the population of German origin.