Castleshaw is a hamlet in the Saddleworth parish of the Metropolitan Borough of Oldham in Greater Manchester, England. It lies amid the Pennines, 2.4 miles (3.9 km) north of Uppermill, 3 miles (4.8 km) west-southwest of Marsden, and 5.3 miles (8.5 km) east-northeast of Oldham.Historically a part of the West Riding of Yorkshire, Castleshaw is most notable for the Castleshaw Roman fort, the remains of an ancient castrum.