I have a quick question about the use of the adj. "longus" in Chapter 12 of Lingua Latina Per Se Illustrata. I am reading through the text mostly as review, but I am unsure of what to think of the word here:
"Marcus: 'Quam altum est vallum castrorum.' Iulius: 'Prope decem pedes altum est, et duo milia passuum longum.'" [M. 'How tall is the wall of the camp'. I.: 'It is near ten feet tall, and 2,000 passus long.']
Is "longus" used here as an adj. in agreement with "vallum" or is it being used almost adverbially in the phrase "2,000 paces long"? I suppose I got the gist of it and didn't question the grammar of the phrase until Pensum A of this chapter which uses a feminine noun with the "mille" construction:
"Via Latina CL...milia pass- long- est." [The Latin Way is 150,000 paces (passuum) long.]
This is where my question about "longus" came up. Should I write that the Via Latina is 150,000 paces "longa est" or "longum est"? I am not sure if "longum" is some sort of adverbial use of the neuter instead of a simple adjective ending.
Multas gratia vobis ago!