Complex sentence: Counts of Blankenburg are documented since 1123; the county is assumed to have developed out of the "Hartingau", original a fief of the Duchy of Saxony, since 1180 of the Bishopric of Halberstadt.
Split into simpler sentences: Counts of Blankenburg are documented since 1123; the county is assumed to have developed out of the Hartingau. The county was originally a fief of the Duchy of Saxony, since 1180 of the Bishopric of Halberstadt.