In the 13th century when the Teutonic Knights began their crusade against the Prussians, some 15,000 people might have lived in the area between the rivers identified by the Knights as Pregel (now Pregolya) and Alle (now Łyna).
The city of Königsberg in Prussia (now Kaliningrad, Russia) was set on both sides of the Pregel River, and included two large islands which were connected to each other and the mainland by seven bridges.