Altstadt (Lithuanian: Senamiestis; Polish: Stare Miasto) was a quarter of central Königsberg, Germany. During the Middle Ages it was the most powerful of the three towns that composed the city of Königsberg, the others being Löbenicht and Kneiphof. Its territory is now part of Kaliningrad, Russia.
Construction of Königsberg Castle began in 1255 during the conquest of Samland by the Teutonic Knights, part of the Prussian Crusade. An initial settlement was founded north of the castle (later known as Steindamm) the following year, but this was destroyed by Sambians during the 1262 Siege of Königsberg. A new fortified settlement developed south of the castle between it and the Pregel River in 1264. Landmeister Konrad von Thierberg granted the settlement Kulm rights on 12 February or 26 February 1286. Although originally named simply Königsberg, the town became known as Altstadt (German for "old town") to differentiate it from the neighboring Neustädte (new towns) of Löbenicht (1300) and Kneiphof (1327). Each town had its own charter, market rights, church, and fortifications.
While some of the original settlers from 1256 remained to participate in the foundation of Altstadt, a greater number of burghers were brought to the region by the locator Gerko von Dobrin. Most of the newcomers were from Lübeck, Lower Saxony, and Westphalia, with others arriving from Pomerania, Mecklenburg, the Elbe basin, Silesia, and western Prussia. The majority of burghers spoke Low German (later Low Prussian), but the languages of administration were those used by the Teutonic Knights, Latin and Central German.