 The monastery of Marienmünster was founded by the counts in 1128.Schwalenberg Castle was built between 1228 and 1231 by count Volkwin III.During the 13th century the territory of the counts was split between several branches, creating the county of Schwalenberg itself (then mainly restricted to a small territory around Schwalenberg Castle), the county of Pyrmont (existing from 1194 until 1495), the county of Waldeck (existing as a principality until 1918) and the county of Sternberg (existing from 1243 until 1377, later disputed between the counts of Schaumburg and the counts of Lippe).