Calvörde Castle was first mentioned in the late 13th century. From 1318 it was held by Duke Otto of Brunswick. The Welf dukes repeatedly gave Calvörde Castle in pawn to local nobles like the House of Alvensleben, while the adjacent settlement ("Flecken") prospered, with town walls, a city council and seal. In 1571 Calvörde passed to the Principality of Wolfenbüttel under Duke Julius of Brunswick. With several surrounding villages and manors, it was reorganised as the Amt Calvörde, which remained an eastern exclave of the Duchy of Brunswick-Lüneburg between the Brandenburgian Altmark in the north and the Archbishopric of Magdeburg in the south.