Roman frontier names

[Nathan Ross]

Quite often it's read as "crossing the limes". But as far as I know the term "limes" didn't mean a 'border line' as such but rather paths or aisles leading into an area.

Yes, I would think so too - it would mean the network of roads, fortifications and military posts, and the surrounding district under military control. So Caracalla 'passed through' the frontier (area) of Raetia to 'erase' the Alamanni.

Regarding the naming of parts, and despite Bede's attempts to distinguish them, I like Collingwood's idea that from an 'architectural point of view' the wall would be the murus and the ditch a fossa, but from a 'tactical point of view' the whole thing might be called the vallum.