A Ghost Wall or Fence is a concept I keep coming across in historical fiction set around the Iron Age or Sub-Roman Britain. Generally, it appears as a boundary made of deceased peoples bones to either keep spirits enclosed or to ward off outside intrusion.
I first came across it in Bernard Cornwell's Warlord Chronicles, a Historical Fiction novel set in Sub-Roman Britain following one of Arthur's warriors as they try to defend against Saxon incursions, we see it used in the line:
Powys's levy stayed on the hill, too scared to cross the ghost fence, …
'A ghost fence might deter the enemy', Taliesin remarked when he had chanted a prayer for the four burning men whose souls were drifting with the smoke to find their shadowbodies.
Later on, a version (at least in name and function) of it appears in The Elder Scrolls: Morrowind where it is used as such:
The Great Ghost Fence (usually shortened to simply 'the Ghostfence') was an enormous shield-like wall surrounding the crater of Red Mountain. Developed to keep the Blight and Corprus monsters contained within the Red Mountain Region, …
And most recently it appears as the title for Sarah Moss's latest book 'Ghost Wall', the Evening Standard's review of it even states that:
A ghost wall is an Iron Age form of defence, where tribes laid skulls out to scare invaders.
The only (pseudo) historical reference I've been able to find is an entry in the Annála Uladh for the year 561 that looks like it could have inspired later writers:
The battle of Cúil Dreimne. It was Fraechán, son of Teimnén, who made the druidic 'fence' for Diarmait. Tuatán son of Dimán son of Sárán son of Cormac son of Eógan cast the druidic 'fence' over them. Maglaine leaped over it and he alone was killed.
I've quickly surveyed Aldhouse-Green's writings (if anyone were going to write about this I strongly guess it'd be her) without any luck nor have I come across any excavation reports describing any similar structures for Iron Age, Roman, or Sub-Roman Britain.
Does anyone know of any archaeological or historical evidence in Iron Age to Sub-Roman Britain for this practice as described? Or is this a purely literary invention and if so does it originate with Cornwell?