"The site of the ancient Segontia ("dominating over the valley") of the Celtiberian Arevaci, now called Villavieja (“old town”), is half a league distant from the present Sigüenza. Livy mentions the town in his discussion of the wars of Cato with the Celtiberians.
The city fell under Roman, Visigothic, Moorish and Castilian rule.

Around 1123 it was taken by Bernard of Agen, its first bishop. Sigüenza played a large part in the civil wars of the thirteenth and fourteenth centuries. The fortress palace of the bishops, an earlier Moorish qasbah, was captured in 1297 by the partisans of the Infantes de la Cerda, and in 1355 it was the prison of Blanche of Bourbon, consort of Peter of Castile. In 1465 Diego López of Madrid, having usurped the miter, fortified himself there." (Wikipedia)