Bridge of el Grajal Monument · Colmenar Viejo, Cuenca Alta del Manzanares, Madrid A medieval bridge of granite ashlar over the upper course of the Manzanares river, beside the M-618 road, within the Regional Park of the Upper Manzanares Basin, next to the flour mills and fulling mills of El Grajal, documented between the 17th and 19th centuries. It was built during the Muslim domination, between the 9th and 11th centuries, as part of an Andalusi military road linking Talamanca de Jarama with the Tiétar valley and connecting defensive watchtowers against Christian incursions. It rests on a single round arch of 10 metres, with a deck 3.34 metres wide —six rassasi cubits, a measurement typical of Islamic bridges— and a humped roadway; it was restored in the 18th century. Upstream stands the El Navallar power station, inaugurated by Alfonso XIII in 1908. Photo: Esetena (CC BY-SA 3.0) What to see and do in Colmenar Viejo