Castell Ewlo is located to the northwest of the town of Hawarden in far eastern Gwynedd. The castle was built during a period when Llywelyn ap Gruffydd was rising in power, but before he was crowned Prince of wales in 1267. Documents dating to 1311 state that Llywelyn ap Gruffydd erected a “castle in the corner of the wood” in 1257. Of all the native castles in North Wales Ewlo is the only with a non spectacular setting. It stands on a promontory overlooking the junction of two streams but is itself overlooked by higher ground to the south. Its position, near the English border, was intended to give Llywelyn control of the road to Chester and the ability to counter the English fortresses of Hawarden and Flint.
There is no mention of Ewlo playing a role in either the war of 1277, which Llywelyn ap Gruffydd lost, or in 1282.

The physical structure of Ewlo is semi-circular. The Upper Ward contains a large Tower, which overlooks a Lower Ward where daily activity of the castle was centered. Circling the perimeter are a rock-cut ditch, steeply sloping embankments, and a curtain wall which encompasses both wards.