“Castell Dinas” in Welsh means “City Castle”, making the name in a way reflective of what is known about the place–which is not much! That said, the castle was once an impressive edifice, so the name is in no way a reflection of its worth, at least at one time.
Though attributed to the Normans, the castle is situated much more like a Welsh castle, as it is located on the top of a hill, with wide views of the surrounding countryside. In fact, the castle is notable for being the highest castle in Wales! It seems to have been built to defend the Rhiangoll pass between Talgarth and Crickhowell.
The site was originally an iron age hillfort, which makes sense given its location, and was originally occupied by native Britons between 600 BC and 50 AD. The stone castle was first built between 1070 and 1075 and is attributed to William fitz Osbern, the first Earl of Hereford, or his son, Robert. This would make it one of the earliest castles built by the Normans to control the Welsh in the March of Wales.
Unlike most of the castles built in this early period, it was built from the start in stone, with a keep surrounded by a curtain wall with square towers. The keep seems to have measured approximately twenty-two meters by 14 meters in length and width. Today, it is a mound with stones protruding from it.
The castle was sacked by Llywelyn Fawr in 1233, after which it was refortified by Henry II, who then gave it to his vassal, Peter fitz Herbert. The remaining standing ruins include the gatehouse, likely dating to the 1233 refortification. Also still visible today are the crumbling curtain wall, along with the surrounding impressive iron age ramparts and fortifications.
The castle was actually captured by Llywelyn ap Gruffydd between 1263 and 1268. There is no further mention of the castle after that until the early 15th century during the period of Owain Glyndwr, whose followers destroyed it rather than let it be used against them by the English.