**EASTERN PRUSSIA – GEOGRAPHY.** – By this name (Ost-Preussen), in German tradition (Eastern Prussia passed to Germany in 1618), is meant the northeastern extremity of the Reich’s territory, bordered by Lithuania, Mazovia, and Western Prussia.
Before 1918, the border with this last region ran from the Frisches Haff to Soldau, lying somewhat to the east of the lower Vistola. After the First World War, with the creation of the Republic of Poland (28 June 1919), the so-called Polish Corridor, which led to Danzig, isolated Eastern Prussia from the rest of Germany. It terminated in the west on the Vistola but had been deprived of the Memel district (annexed by Lithuania). Within these limits, Eastern Prussia measured 36,991 sq. km., with a population, in 1939, of 2.4 million inhabitants (65 per sq. km.). The territory is almost entirely flat or gently undulating (with elevations rarely exceeding 300 m.), dotted with numerous lakes, ponds, and peat bogs, and opens onto the Baltic with a low coast fringed by long sandy spits (Ger. Nehrung, Pol. Mierzeja). Once almost entirely covered by forests (now reduced to barely one-sixth of the total area), Eastern Prussia had been transformed by German colonization (dating back to the 13th century) into an agricultural region that, though not entirely fertile, produced cereals in considerable quantities, as well as potatoes, sugar beets, and vegetables. Livestock breeding (cattle and horses) was also well developed. In the population, the German element stood out from the Masurians, of Slavic stock (just over 120,000, predominant in the inland regions), though they too had become deeply Germanized; above all, the major urban centers (with the capital Königsberg, which exceeded 100,000 inhabitants) had assumed a distinctly German character.
Under the Potsdam Agreements and the Treaty of 16 August 1945 between Poland and the U.S.S.R., Eastern Prussia was divided into two parts: the southern portion (Masuria), incorporated into the new Republic of Poland, where it essentially forms the voivodeship of Olsztyn (Allenstein; 20,994 sq. km. with 442,000 inhabitants); the northern portion, annexed to the U.S.S.R. as the Kaliningrad autonomous district (Königsberg; 10,000 sq. km. with 400,000 inhabitants), dependent on the R.S.F.S.R. The border between the two units runs roughly along the 54° 20' N parallel.
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**EASTERN PRUSSIA – HISTORY.** – The name Eastern Prussia, rather than designating a geographical unit, is a historical-political definition dating back to 1772, when, after the first partition of Poland, Frederick II of Prussia obtained Pomerelia, to which he gave the name of Western Prussia. The territories of the former Duchy of Prussia, the political center of the state established by the Teutonic Order in the Middle Ages, located to the east of Western Prussia, thus received the name Eastern Prussia.
After the migrations of the Germanic peoples toward the West, the territory now known as Eastern Prussia was inhabited by a Baltic people, the Prussians, pagans of a markedly warlike disposition. Attempts were made to convert them to Christianity, but both Adalbert of Prague and Bruno of Querfurt, who undertook this mission around the year 1000, met with violent deaths and suffered martyrdom. Later, the kings of Poland also strove to subjugate the Prussians, but without success. More concrete results were achieved by the evangelizing mission begun in the early 13th century by the Cistercian monk Christian, who in 1216 was consecrated Bishop of Prussia. However, as Prussians hostility grew, Duke Conrad of Masovia turned around 1226 to the Teutonic Order for assistance. To enable the Order to subdue the infidels, Duke Conrad donated the Culmerland (Terra Colmenis: Ger. Kulm, Pol. Chełmno), probably as an operational base for the crusade against the Prussians, to the Grand Master of the Order, Hermann of Salza. The intervention of the Order swiftly led to the conquest