Because the Baltic tribes inhabiting Prussia never formed a common political and territorial organisation (a state), they had no reason to adopt a common ethnic name. Instead they used the name of the region from which they came - Galindians, Sambians, Bartians, Nadrovians, Natangians, Scalovians and Sudovians. It is not known when and how the first general names came into being in the lands that did not have a tribe name tradition such as Pomesania, Pogesania or Sasinia in the western peripheries of the Prussian settlements.
Parts of the Baltic region retained wilderness areas for longer than almost anywhere else in Europe. Tacitus may have been referring to peoples living in what was later East Prussia when, in AD 98, he wrote of the Aesti in his Germania. These people may have been those later known as the Aesti-Prussi, who lived between the Vistula and Niemen rivers and spoke a Baltic rather than a Germanic language. Tacitus referred to all the tribes living near the Mare Suebicum, or the Baltic Sea, under the collective name of Suebi, a broad term which included also various peoples to the south, including the Lombards, Rugi, Burgundians, Semnoni, Vandals, Lugi, Silingi, Goths and others who made their homes near the Elbe, Oder and Vistula rivers.
16th century histories of Prussia link the name of the "Prussai" or "Prussi," and thereby Prussia, to a place called "Prutenia". According to these histories, most likely based on heroic sagas, Pruteno (or Bruteno) was a priest king, brother of the legendary king Widewuto or Waidewut, who lived in the late 10th century. The regions of Prussia and their peoples are said to bear Widewuto's sons' names. These peoples include the Yatvingians and Sudovians. In the first half of the 13th century bishop Christian of Prussia recorded the history of a much earlier era. Adam of Bremen mentions Prussians in 1072.
The foundation of the Holy Roman Empire allowed the Ottonian Emperors the opportunity to continue to expand eastwards the holdings they had inherited from the East Frankish kingdom. They achieved this largely through continuing the Carolingian policy of co-opting local Slavic chieftains or ambitious war-leaders into a system of mutual defence and allegiance. This policy not only bound former enemies to the Emperor, but also prevented any of the Emperor's West Frankish leading men from expanding their own power bases eastward.
It is not surprising, then, that when the Duchy of Poland was established (c.962), the Polish dukes attempted to increase their territory. Where expansion offered the opportunity to convert pagan peoples to Christianity, the support of both Emperor and Pope was almost guaranteed. In 997, Boleslaus I, then duke of Poland, gave military protection to Saint Adalbert of Prague when he went to convert the Prussians. The Prussians resisted these attempts at conversion, which have been seen as an attempt to weaken their independence. Like many other missionaries, Adalbert was martyred by those he wished to convert.
The western part of Pomerelia-Prussia was christianised by Otto of Bamberg. In 1209 Pope Innocent III commissioned the Cistercian monk Christian of Oliva with the conversion of the still-pagan eastern Prussians. Christian afterwards became the first bishop of Prussia.
In 1220 Conrad of Masovia invaded and even reconquered some of the Prussian territory in the Kulmerland. When the Prussians attempted to re-take their own territory, Conrad called on the pope and the emperor for a Crusade. The results were edicts calling for Crusades against the "marauding, heathen" Prussians. Many of Europe's knights joined in these Crusades, which lasted sixty years. In 1243, the Papal legate William of Modena divided Prussia into four bishoprics, Kulmerland, Pomesania, Ermland (Warmia), and Samland under the archbishopric of Riga.Prussia in the Middle Ages