I have a question in relation to stress for second declension nouns ending in "ius" and "ium" in the genitive and vocative.
Some sources, for example Allen and Greenough say to stress the same syllable in the genitive and vocative as in the nominative. So Vergilius with the stress on the 'gi' would become Vergili in the genitive and vocative, and keep the stress on the 'gi', even though this violates the usual stress rule?
However Vox Latina says:
Similar considerations apply to the trisyllabic genitive and vocative forms of words like Valerius, which, according to Gellius, were both accented in his time (second century A.D.) as Valeri. But this observation is not supported by other writers, and there is no metrical evidence for the penultimate accentuation in Plautus or Terence.
What is the commonly accepted or orthodox way to stress the ius/ium words in the genitive or vocative?
Wheelock uses the later version of latin in which the genitive would be Vergilii, but that still leaves the issue of what to do with the vocative Vergili.