Prussia is a historical region in Central Europe on the south-eastern coast of the Baltic Sea that ranges from the Vistula delta in the west to the end of the Curonian Spit in the east and extends inland as far as Masuria, divided between Poland (Warmian–Masurian Voivodeship), Russia (Kaliningrad Oblast) and Lithuania (Lithuania Minor). This region is often also referred to as Old Prussia.

Tacitus's Germania (98 AD) is the oldest known record of an eyewitness account on the territory and its inhabitants. Suiones, Sitones, Goths and other Germanic people had temporarily settled to the east and west of the Vistula River during the Migration Period, adjacent to the Aesti, who lived further to the east.

Overview

The region's inhabitants of the Middle Ages were first called Bruzi in the brief text of the Bavarian Geographer and have since been referred to as Old Prussians, who, beginning in 997 AD, repeatedly defended themselves against conquest attempts by the newly created Duchy of the Polans. The territories of the Old Prussians and the neighboring Curonians and Livonians were politically unified in the 1230s under the State of the Teutonic Order. The former kingdom and later state of Prussia (1701–1947) derived its name from the region.

The Teutonic Knights invaded and annexed the region of Pomerelia from Poland into their monastic state, which already included historical Prussia, located east of the region. After the acquisition of Pomerelia in 1308–1310, the meaning of the term Prussia was widened in the German terminology to include areas west of the Vistula, including Vistula/Eastern Pomerania, although it was never inhabited by Baltic Prussians but by the Slavic Poles. After the area was reintegrated with Poland in 1466 both names were in use: Pomerania was used when referring to the Pomeranian Voivodeship (Gdańsk Pomerania) and the Chełmno Voivodeship, while Royal Prussia was used as the name of the wider province, which, however, also included the Malbork Voivodeship and the Prince-Bishopric of Warmia, covering the Prussian historical areas of Pomesania, Pogesania and Warmia, the only actual Prussian territories of the province, while the rump Teutonic state, called the Monastic Prussia thereafter, formed a part of Poland as a fief, finally secularised in 1525 to become the Lutheran Ducal Prussia.

Brandenburg Electors obtained the separation of the Duchy of Prussia from Poland in 1660, taking advantage of the Russo-Swedish Deluge, and merged it with the Electorate of Brandenburg to form Brandenburg-Prussia, shortly thereafter becoming the Kingdom of Prussia. Subsequently, it entered into an alliance with Austria and Russia, invading Polish territories of Royal Prussia, annexing and dividing it, with its bulk (including Pomerelia and the Malbork Land comprising northern parts of Pomesania and Pogesania) forming (along with the northern part of Greater Poland detached from the Grand Duchy of Posen) the Province of West Prussia, while Warmia was assigned to East Prussia, with both West and East Prussia remaining outside the German Confederation. In contrast, the Lauenburg and Bütow Land was annexed in 1777 immediately into the Province of Pomerania, but remained outside the Holy Roman Empire and was incorporated in 1815 only into its successor, the German Confederation, continuing to be a part of the Diocese of Chełmno.

The Province of East Prussia (the original Prussia) and the annexed Polish territories turned into the Province of West Prussia were merged in 1829 to form a single Province of Prussia, a part of the kingdom remaining outside of Germany until the creation of the North German Confederation in 1866 during the unification of Germany. The merged territory was, however, again split into East and West Prussia in 1878.

East Prussia, West Prussia, the Province of Posen and the Starostwo of Draheim were annexed by Germany upon the formation of North German Confederation in 1866 and became a target of aggressive Germanization, German settlement, anti-Catholic campaigns (Kulturkampf), as well as disfranchisement and expropriations of Poles.

After the Treaty of Versailles, only the predominantly German-speaking western and eastern rim of the former West Prussia remained a part of Germany, forming part of the rump province of Posen-West Prussia (except for the Lauenburg and Bütow Land remaining a part of the Province of Pomerania, as well as the Regierungsbezirk Westpreussen which was made part of East Prussia), while its bulk was awarded to the recreated Polish state.

On the other hand, only minor part of East Prussia around Działdowo was transferred to Poland, the Klaipėda Region formed a free city supervised by the League of Nations, annexed following the Klaipėda Revolt by Lithuania but reclaimed by Germany in 1939, while the bulk (including entire Warmia and most of Masuria) remained within the Free State of Prussia, a successor of the Kingdom of Prussia and a constituent part of the German Weimar Republic, following the 1920 East Prussian plebiscite.

Since its conquest by the Red Army with evacuation and expulsion of the German-speaking inhabitants in 1945 in accordance with the Potsdam Agreement, the region of Prussia remains divided between northern Poland (most of the Warmian-Masurian Voivodeship, and the four counties of Pomeranian Voivodeship east of Vistula), Russia's Kaliningrad exclave, and southwestern Lithuania (former Klaipėda Region).

The Greek explorer Pytheas (4th century BC) may have referred to the territory as Mentenomon and to the inhabitants as Guttones (neighbours of the Teutones, probably referring to the Goths). A river to the east of the Vistula was called the Guttalus, perhaps corresponding to the Nemunas, the Łyna, or the Pregola. In AD 98, Tacitus described one of the tribes living near the Baltic Sea () as Aestiorum gentes and amber-gatherers.

The Vikings started to penetrate the southeastern shores of the Baltic Sea in the 7th and 8th centuries. The largest trade centres of the Prussians, such as Truso and Kaup, seem to have absorbed a number of Norse people. Prussians used the Baltic Sea as a trading route, frequently travelling from Truso to Birka (in present-day Sweden).

At the end of the Viking Age, the sons of Danish kings Harald Bluetooth and Cnut the Great launched several expeditions against the Prussians. They destroyed many areas in Prussia, including Truso and Kaup, but failed to dominate the population totally. A Viking (Varangian) presence in the area was "less than dominant and very much less than imperial."

The territory was identified as Brus in the 8th-century map of the Bavarian Geographer and Bruzze/Pruzze/Przze in the Dagome iudex. Adam of Bremen mentions Prussians as Prusos/Pruzzi in 1072., while Gallus Anonymous mentions Prussia in his Gesta principum Polonorum in 1113. In the first half of the 13th century, Bishop Christian of Prussia recorded the history of a much earlier era. In Neo-Latin the area is called Borussia and its inhabitants Borussi.

thumb|Medieval depiction of Prussians killing [[Adalbert of Prague|Saint Adalbert, the missionary bishop; part of the Gniezno Doors, ]]

After the Christianisations of the West Slavs in the 10th century, the state of the Polans was established and there were first attempts at conquering and baptizing the Baltic peoples. Bolesław I Chrobry sent Adalbert of Prague in 997 on a military and Christianizing mission. Adalbert, accompanied by armed guards, attempted to convert the Prussians to Christianity. He was killed by a Prussian pagan priest in 997.

In 1015, Bolesław sent soldiers again, with some short-lived success, gaining regular paid tribute from some Prussians in the border regions, but it did not last. Polish rulers sent invasions to the territory in 1147, 1161–1166, and a number of times in the early 13th century. While these were repelled by the Prussians, the Chełmno Land became exposed to their frequent raids. The Knights were expected to fight the inhabitants of Prussia in exchange for a fief of Chełmno Land. Prussia was conquered by the Teutonic Knights during the Prussian Crusade and administered within their State of the Teutonic Order, which begins the process of Germanization in the area. Bishop Christian had to deal with the constant cut-back of his autonomy by the Knights and asked the Roman Curia for mediation. In 1243, the Papal legate William of Modena divided the Prussian lands of the Order's State into four dioceses, whereby the bishops retained the secular rule over about one third of the diocesan territory:

  • Bishopric of Chełmno (Chełmno Land and Lubawa Land)
  • Bishopric of Pomesania (Pomesania)
  • Bishopric of Warmia (state)/ Diocese of Warmia (ecclesiastical ambit)
  • Bishopric of Samland (Sambia)

all suffragan dioceses under the Archbishopric of Riga. Christian was supposed to choose one of them, but did not agree to the division. He possibly retired to the Cistercians Abbey in Sulejów, where he died before the conflict was solved.

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Image:Piotr Dusburg chronicle.png|The Chronicon terrae Prussiae is the first major chronicle of the Teutonic Order in Prussia.

Image:Castillo de Malbork, Polonia, 2013-05-19, DD 04.jpg|The political center of Prussia until 1457 was the Ordensburg Marienburg in what is now Malbork, Poland.

Image:Teutonic Order 1260.png| Monastic State of the Teutonic Knights

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The city of Königsberg (modern Kaliningrad) was founded in 1255, and joined the Hanseatic League in 1340, thus connecting Prussia to the European trade network spanning via the North Sea and the Baltic Sea. In 1492, a life of Saint Dorothea of Montau, published in Marienburg (Malbork), became the first printed publication in Prussia.