Castelvecchio Subequo (also Subrequo and Subrego; Latin: Superaequum, Superequum) is a comune and town in the province of L'Aquila in the Abruzzo region, central Italy, at the feet on Mount Sirente.

Ancient Superaequum was a town of the Paeligni, one of the three which possessed municipal rights, and among which the territory of that people was divided.

It received a colony of veterans, probably under Augustus, to which a fresh body of colonists was added in the reign of Marcus Aurelius.

After the conquest of southern Italy by the Lombards, it was known as Onuffolo or Nuffoli, returning to its former name under the Normans.

It is on a hill on the right bank of the Aterno river, and about 7 kilometres (4 mi) on the left of the Via Valeria.