the answer is simple: because dies is feminine here. dies can be of either gender. In prose, it usually means something like "appointment" if it is feminine; in poetry the genders are usually completely interchangable.Tactixian dixit:Die constituta causae dictionis
Given: On the day appointed for the pleading of his cause
How does this work? dies, diei is masculine, so how could constituta modify it?
I had "On that day, the matter of pleading the cause having been decided [(re) causae dictionis constituta]"
that would leave quam ob rem strandedincitata armis ius suum exequi conaretur
Given: incensed at this act, was endeavoring to assert its right by arms
Could incitate armis not mean "incited to arms"?