ST7681 : Tower near Old Sodbury Not a folly but you may be forgiven for thinking it.
The blackened appearance of this castellated structure gives the clue. It is the top of an air shaft, one of six, giving vent to the Sodbury Rail tunnel beneath.
The tunnel is 4433 yards long on the Swindon - Patchway - Newport line of the old G.W.R.
The earthworks next to it is spoil dug from the tunnel during construct and removed via the air shaft.