 Located in the Apennines between the Ufita Valley and Daunian Mountains, the town is part of the Roman Catholic Diocese of Ariano Irpino-Lacedonia.Its territory borders the municipalities of Carife, Flumeri, San Nicola Baronia, Sturno, and Trevico.The name of the town comes from the word Castello (from the Latin "Castellum") due to the existence dating back to the Norman era, of an impenetrable fort in the highest part of the area, Trevico, above sea level, which dominated the town and surrounding areas.