Less than 100 yards north of the fort was (is?) a spring. (I can see it on an 1867 map at SZ314970).
Buckland Spring.
Near Buckland, north of Lymington, there was a small spring to the north of the great earthwork which was for generations held in great estimation for its reputative curative properites in ophthalmic disorders.
In RC Hope’s ‘Legendary Lore of the Holy Wells of England’ (1893) – he’s quoting from the Hampshire Field Club v2, pt i., p.47.