Ruthin Castle is a medieval castle fortification in Wales, near the town of Ruthin in the Vale of Clwyd. It was constructed during the late 13th century by Dafydd ap Gruffydd, the brother of Prince Llywelyn ap Gruffudd, on a red sandstone ridge overlooking the valley. Part of the ancient walls still remain and now form part of the Ruthin Castle Hotel.HistoryRuthin Castle occupies a site that was first used as an Iron Age fort. In 1277, Edward I of England granted the land to Dafydd ap Gruffydd in gratitude for his assistance during the invasion of North Wales. It is unclear whether there was an existing fort on the site or whether Dafydd established the castle. The castle was originally given the Welsh name of Castell Coch yn yr Gwernfor (Welsh Red Castle in the Great Marsh).The castle was most notably the base of that branch of the noble de Grey family accorded the title "Barons Grey de Ruthyn" and the head of their marcher lordship of Dyffryn Clwyd. It was a base for Reginald Grey, 3rd Baron Grey de Ruthyn – the man who could be said to have sparked the rebellion of Owain Glyndŵr.