Partrishow, also known as Patricio, Patrishow, or by its Welsh names Merthyr Isw and Llanisw, is a small village and historic parish in the county of Powys (historically Brecknockshire), close to its border with Monmouthshire. It is in the valley of the Grwyne Fawr, in the Black Mountains of South Wales, within the Brecon Beacons National Park.