Roman frontier names

[Nathan Ross]

This 1988 essay by Benjamin Isaacs is very thorough on the meaning of limes and how it developed from the 1st to the 3rd century, and includes all the quotes mentioned here so far and a number of others:

The Meaning of the Terms Limes and Limitanei

Isaacs proposes that the word initially referred to a military road (mainly through wooded terrain, it seems), with the secondary meaning of a boundary, not necessarily a frontier one. Only in the 3rd century did the term come to refer specifically to the frontier itself in a general sense, and was later extended (which was the bit I remembered!) to mean the frontier zone or hinterland area as well.

Incidentally, Isaacs also mentions that the Antonine Itinerary refers to Hadrian's Wall as 'the vallum'.

[Coroticos]

Thanks guys.

So far, then, we have Hadrian's Wall (or the combined frontier features of which) being referred to as A/The vallum in:

The Ilam pan (possibly).

Mike's inscription from Kirksteads.

The Antonine Itinerary.

And of course, the Notitia Dignitatum (for the west) Ch. 40 lists the 24 army units 'along the line of the Wall' as 'per lineam valli'. Though it is true that some of those units are based at the coastal forts of Cumbria/Lancashire, going beyond the strictly accepted western end of 'the wall', at Maia/Bowness.

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Similarly, the 'vallum ditch' does not continue east between Newcastle and Wallsend, so is not a continuous part of the frontier

From Newcastle to Wallsend the ditch isn't needed, the wall runs close along the river.
From the bridge at Newcastle to Wallsend would slready be a closed military zone.

That's true. Which then implies that the vallum performed the same function as the river Tyne, perhaps. It certainly would have functioned as a 'moat' to prevent attack by land from south of the river. Although of course, at the same time, it would have actually provided a 'highway' for water-borne raiders to attack the rear of the military zone, if they rowed/sailed up-river. Maybe that was why the Tigris Boatmen were eventually based at the mouth of the Tyne, at South Shields, (in the early 4th c.) to prevent Pictish (or even, by that time, Saxon) pirates doing just that. 

Interestingly, Raymond Selkirk sees the 'vallum' (the rearward-facing ditch plus mounds) as a 'rearguard', to prevent an enemy, having breached the front of the wall, from then being able to attack along its rear. Though perhaps it would have been better at defending from an initial rearward or flanking attack than from a frontal breach which then posed a threat to the rear. Since, once an enemy had breached either the frontal wall or the rearward ditch, they would have been able to used the military road to spread along the frontier between the two lines of defence.