I have now taken the map showing the boundaries of Selwood Forest, from Michael McGarvie’s ‘The Bounds of Selwood’ (this shows the smaller, western section in Somerset, as established according to the perambulations, as well as the main section within Wiltshire), and superimposed it – they didn’t quite fit – over a map of the Hundreds of Wiltshire. This is just the southern half of the forest, but including Edington.
Now, consider the words of Asser, De rebus gestis Ælfredi:
Iterumque in septima hebdomada post Pascha ad Petram Aegbryhta, quae est in orientali parte saltus, qui dicitur Seluudu [ … ] equitavit …
Also, the Anglo-Saxon Chronicle (these two sources interdependent), Anno 878:
Þa on þære seofoðan wiecan ofer Eastron he gerad to Ecgbryhtes stane be eastan Sealwyda …
Well, take a look at the map. I’ve added green dots to show the extent of the forest. How can anyone imagine that Penselwood is in the east of the forest? It just isn’t. It’s in the west. The question is not where Egbert’s Stone was, but why did most people think it was at Penselwood?
Each Hundred had its meeting-place. The blue Hundred, bottom left, is Mere Hundred;. Penselwood was actually in Wincanton Hundred. I haven’t found a source which identifies where all the meeting-places were, but Wincanton was probably the meeting-place for Wincanton Hundred, and Mere for Mere Hundred. These would have been where each Hundred assembled its fyrd. Still no connection with Penselwood.
I’ve shown – very roughly (I think it should have been slightly further to the west) – the extent of Salisbury Plain nowadays. This suggests that Alfred’s final line of march was over the Plain. Also the pass (the two small blue lines) near Alfred’s Tower which Colt Hoare suggested was the route Alfred took after leaving Athelney.