I am currently writing a small geography of the Roman Empire at its greatest extent (in the year 117 AD, under Emperor Trajan) in an effort to practice my composition skills. So far everything has been going well, however, via a discussion in CONLOQVIVM, a very specific question came up concerning cardinal directions.
In my writing, I am currently things similar to the following phrase a lot (in Latin of course; this is simply an example):
(written) Gaul is found to the north of Italy.
(or, more explicitly phrased) Gaul is found in the region north of Italy.
In Latin, I would usually write the above as follows, using ad plus a cardinal direction in the accusative and a genitive or in plus a cardinal direction in the ablative and a genitive, like so:
Gallia ad septentriōnem Ītaliae invenitur.
Gallia in septentriōne Ītaliae invenitur.
To me, when writing out my Latin, without trying to think too much in English about meaning or phrasing, this is what felt natural to me. However, I can't help but feel (as a result of it being pointed out by @JoonasIlmavirta and @Cerberus in CONLOQVIVM) that this isn't quite right and that the Romans probably would have had a more idiomatic way of phrasing this.
In short, what would be the appropriate or idiomatic way of phrasing the English concept of to the [cardinal direction] of [something]?