Roman frontier names

[Lupianus]

Nathan, sounds perfectly possible.

Michael, true, it's an interpretation. But Tacitus uses the term "limes" on very few and quite specific occasions, where the common "barrier" or "frontier" translations don't really work (he would use "terminus" for the latter). Here's what others have found, namely Wolfgang Moschek (Der Römische Limes. Eine Kultur- und Mentalitätsgeschichte. Speyer 2011), no exhaustive list:

Annales 1.50
at Romanus agmine propero silvam Caesiam limitemque a Tiberio coeptum scindit, castra in limite locat, frontem ac tergum vallo, latera concaedibus munitus
But the Roman [general] in a forced march, cut through the Caesian forest and the aisle which had been begun by Tiberius [=to reopen an existing road], and he pitched his camp on that aisle, front and rear being defended by a rampart, flanks by timber barricades.

Annales 2.7
et cuncta inter castellum Alisonem ac Rhenum novis limitibus aggeribusque permunita
And all the land between Aliso and the Rhine was thorougly secured by new aisles and dykes [=pioneers building roads].

Histories 3.21
dextro octava per apertum limitem, mox tertia densis arbustis intersaepta
From the right [came] the Eighth [legion] through an opened aisle, and then the Third, separated by some thick brushwood [=they are in a forest area].

I'm not saying that Tacitus used a fixed, universally accepted terminology here, rather that his usage appears to be quite consistent.