Castle Ditches is the site of an Iron Age trivallate hillfort in the south-east of Tisbury parish in Wiltshire, England.

It is probable that its ancient name was Spelsbury; it was referred to as Willburge in Tisbury's charter of 984 A.D.[1] Its shape is roughly triangular, and follows the contours of the small hill upon which it sits.

The earthworks comprise a triple row of ramparts and ditches, now covered on three sides by woodland.

There is a large entrance towards the south-east, where there is the shallowest incline of the hill; but there is also a narrow slit on the opposite side.

The area within the site encompasses nearly 24 acres (9.7 ha), and the greatest height of the ramparts is about 40 feet (12 m).