Ulrich von Sigmaringen, Ludwig II von Sigmaringen-Spitzenberg and Manegold von Sigmaringen-Spitzenberg. The three brothers, Ulrich, Ludwig and Mangold von Sigmaringen are named as the founders of the 11th-century St. George's Abbey in the Black Forest. From 1133 until 1170 Rudolf von Sigmaringen-Spitzenberg, the son of Ludwig II, ruled at Sigmaringen. In 1183 Graf Ludwig von Sigmaringen-Spitzenberg-Helfenstein, the son of Rudolf, is mentioned at the castle. In 1147 Ludwig as well as his father Rudolf and brother Ulrich II von Sigmaringen-Spitzenberg are mentioned in a document of Walter von Dillingen, Prince-Bishop of Augsburg, as lords of Spitzenberg-Sigmaringen. Under the Helfenstein family, until 1290 Under the Helfenstein family, the castle was renovated around 1200. The castle was totally rebuilt with buckel stones (squared-off stones with a rounded outer surface). Between 1209 and 1258 the castle was occupied by Graf Gottried von Sigmaringen-Helfenstein and his son Graf Gebhard von Sigmaringen-Pietengau. In 1258 the cousin of Graf Gebhard, Graf Ulrich II. von Helfenstein, became the owner of Burg Sigmaringen. Later, Ulrich's daughter Agnes married Graf Ulrich I. von Montfort. Following the marriage in 1272, Sigmaringen was owned by the Counts of Montfort. Then, in 1290 Graf Hugo V. von Montfort, son of Ulrich I, sold the castle and the city of Sigmaringen to Albrecht and Rudolf von Habsburg. Before 1325 Duke Luipold von Habsburg sold the castle and the county of Sigmaringen to the Count of Württemberg. Werdenberg family 1399–1534 Finally in 1399 Count Eberhard von Württemberg granted the castle and county of Sigmaringensein as well as the county of Veringen in Margraviate of Austria, to his uncle and liegeman Count Eberhard III. von Werdenberg (1387–1416) as a fief. His son Count Johann IV. von Werdenberg (1416–1465) and his wife Countess von Württemberg (disinherited by the House of Württemberg), in 1459 inherited the castle and county of Sigmaringen. To protect his land, in the following year he declared Sigmaringen an Austrian fief. From 1460 until 1500 the Counts von Werdenberg renovated the Burg (a military fortress) into Schloss Sigmaringen (a fortified residence), and expanded it to the dimensions which remain today. Toward the end of the 15th century they built two long, angular buildings in the north east. Then, in the early 16th century another wing was added to the west. The two round towers that flank the entrance to the castle also date from this time Hugo IX. zu Sigmaringen (1459–1508), son of