The county of Cerezo on the eastern frontier Historical milestone · Cerezo de Río Tirón, Montes de Oca, Burgos Cerezo was head of a Castilian county and a piece of the defensive line that, with Ibrillos, Grañón, Cellorigo, Lantarón and Pancorbo, closed the eastern end of Castile; its castle, of the ninth century, was remodelled in the fifteenth. siglo X Photo: Maestro García (CC BY-SA 4.0) What to see and do in Cerezo de Río Tirón