The boundary between Thuringia and the Sorbs was defined as the Saale river by Einhard, writing in the 830s: ("the river Saale, which divides the Thuringii and the Sorbs"). Erfurt was then the chief economic centre of eastern Thuringia. The Sorbian March probably (loosely) included the land east of the Saale as far as the Elster and the Pleisse, which might have been controlled by castles. The Sorbian March may have been only the area west of the Saale, east of it, or on both sides.
