Word order in general being at the whim of the writer is the bane of the modern learner, although we can be sure that this is a stylistic device and that the spoken word order would have been much more standardised. There's a wonderful line in "The Loom of Language" (wonderful book, wish I could find my copy) berating "the crossword puzzles of Cicero" vs the language he'd use to bawl out his slave.

> the grammar (and thus the meaning) is sometimes driven by the meter

What do you mean by this? The closest I can come to making sense of it is that some Latin words obligatorily appear as the second word in the sentence, but it seems like you must mean something different?

I'm guessing that the issue is just that in poetry many authors are willing to use word orders and constructions that would otherwise be regarded as questionable or ungrammatical—"metri causa".

I'm pulling from my studies of ~10 years ago, but IIRC there are points (noun and adjective endings?) where diacritical marks can change the meaning of the sentence. Unlike, say, Spanish, these marks are not written, and frequently have to be interpreted from language cues, including the meter.

That's basically correct -- some case endings differ only by vowel length and are therefore not distinguished in standard Latin writing, which doesn't indicate vowel length in any way. (Old Latin writing sometimes did.) "Via", in nominative case, meaning "the road" as the subject of a sentence, is written identically to "via", in ablative case, meaning "by the road", but the 'a' of the ablative case ending is longer.

However, you can't describe this as "the meter driving the grammar". The grammar requires the same cases and vowel lengths regardless of the meter you're trying to achieve. Rather, we modern-day people reading Latin poetry can use the meter to help us determine what was originally written. All of the causal influence is from grammar to meter, not the other way around.

That's pretty much what I meant... A naturally fluent reader of Latin poetry would have had to follow the same process of inferences (drawing from a far more intuitive and internalized model of the meter, of course).

Quite. Though, if by any chance you have reached a sufficient mastery of English prosody to understand the iambic pentameter, the dactylic hexameter really isn't such a stretch, notwithstanding one being based on stress and the other weight.

I so enjoyed the pattern-matching puzzle that I found preparing for the AP Latin (Virgil) exam to be.