This univallate hill fort dates from the late Bronze Age / Early Iron Age. Can it really be a fort? It looks so precarious on the map, crossing a thicket of contour lines. Naturally well defended at least. (see details on MAGIC at http://www.magic.gov.uk/rsm/24008.pdf
'Trendle' (like the Trundle, one assumes) comes from the Middle English for 'wheel', which in turn comes from the Old English for 'circle' - indeed, the shape of the fort.
It's said that here on Bicknoller hill 'the woman of the mist' can be seen (apparently, according to Ruth Tongue in 'Somerset Folklore' 1965, 'in recent years'). She sounds rather like the Scottish Cailleach (see Schiehallion) as "she herds the red deer. Sometimes she appears as an old frail crone, sometimes as a great misty figure."
Possible Iron Age enclosure situated on a steep west facing slope of Bicknoller Hill. It is defined by a bank which encloses a sub-circular area measuring 97m by 87m. The enclosure is morphologically similar to the so called "hill-slope" enclosures common on Exmoor. The function of the enclosure is unclear as the steepness of the slope suggests it would be impractical as a settlement or even as a stock enclosure. Although it has a substantial rampart it is not in a particularly defendable topographical situation but it is highly visible and impressive when viewed from the valley below. A possible cross-ridge a dyke situated to the north east of the enclosure may be an associated feature although there is no actual evidence for this.