In yet another twist of coincidence (or not?) this fortress is known locally as the tower of Doña Urraca, whose namesake was the evil magpie sister in the film version of El Cid, although not so bad in real life apparently.
The name stuck after Urraca (according to legend) was stuck inside a wall (a quaint medieval punishment) after refusing to marry the Príncipe de León, due to a crush (no pun intended) she had on a local shepherd.
It is at this castle that a Moorish force turns up to drag off 100 maidens, fulfilling their part of a signed treaty; a treaty broken by Fernán, who manages to swap the maidens for his soldiers, proving that the Moors were just getting what they deserved as they were slaughtered.