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