Thank you very much Kevin, Yes I have a copy of the atlas, I will consult it again - I find it a bit complicated but, you're right, the maps are good.
I am very grateful for your kind assistance,

Please can I ask one more question - why was the 'bridge of boats' over the Adour regarded as so special? The army had crossed wide rivers before. How did this crossing differ from the pontoons in use, do you know?

Thanks as always, Chrissy