There was a very interesting article about cursuses in the March edition of British Archaeology.
Here it is:
http://www.britarch.ac.uk/ba/ba69/feat1.shtml
baza
That's really interesting, looks like my ideas were not so odd as I thought - linking the rivers etc.
Right, I'll expand on my "the early years theory" later.
I have also come up with a "Copist" theory explaining exactly why Thorborough is where it is and why it is perhaps the most important site in Britain!