Originally Posted by
Ludens
A meta-strategic question: do you want to neutralize the Sweboz or take their land? The latter is not very profitable: the cities are poor and distances great, meaning you need to cover a long border with garrisons for little financial reward. The Sweboz regionals available to the Celts are nothing to write home about, and IIRC you can get better German units as mercs.
If your objective is merely to neutralize the Sweboz, why don't you simply garrison the river-crossings? They will waste their armies on your defensive line and you are free to take on more dangerous (and richer) foes.