About 98 A.D., the Roman historian Publius Cornelius Tacitus in his work “Germania mentions THE AISTIANS (Aestorum gentes) living east of the Germanic tribes. In the middle of the 19th century the Aistians were named BALTS.

About 960 the ethnonym of the Prussians Bruzi living at Aest Sea was mentioned in Description of Towns and Regions of the Northern Danube Land prepared by a Bavarian geographer. About 1074, Adamus Bremenensis mentioned Sembi vel Pruzzi (Sembians or Prussians). 

1226. Teutonic Order (German Military Order of Knights), which was expelled from Hungary in 1225 for their excessive demands, are invited by a Polish Duke Conrad of Mazowia, with lands on the lower reaches of the Vistula river, to help him fight the pagan Prussians. In order to avoid the bitter experience of Hungary and to secure the Order’s position, its Grand Master Hermann von Salza obtained from the Hohenstaufen Emperor Frederick II the so-called Golden Bull of Rimini as a legal basis for the settlement. By this charter, Frederick confirmed to Hermann and to the Order not only the lands to be granted by Conrad, but also those that the knights were to conquer from the Prussians. Later (1234), Hermann also secured privileges from Pope Gregory IX, which can be regarded as the second foundation charter of the Order’s Prussian State: the papacy was ready to accept the Order’s current and future conquests as the property of the Holy See and to grant them back to the Order in perpetual tenure. 

1230. By the act of Kruchwitz of 16 June, Conrad of Mazowia grants to the Order the lands of Kulm, which never belonged to Mazowia. Pope Gregory IX, who in the autumn of the same years calls for a crusade against the Prussians, confirms this illegal grant. 

1231. Combined German and Polish forces cross the Vistula River and begin the invasion of Prussian lands. During the next fifty years, having advanced from the lower Vistula River to the lower Nemunas River and having exterminated most of the native Prussian population (especially during the major uprising of 1260 – 1274), the Order firmly established its control over Prussia. 

1250. The Order build their first castle in the Koningsberg region at Balga on the Aistian Lagoon (now, Vistula Lagoon) in place of the Vundenava castle of a Prussian tribe Varmi.