Domenico Comparetti, in Vergil in the Middle Ages, relates a fascinating anecdote about the spiritual Nachleben (or wistful longing after same) of Vergil:
Hence [Vergil] is the first of those whom Dante, that faithful interpreter of the religious sentiment of the middle ages, would not put among the damned, but placed among those whose one involuntary fault was that they were not baptized. This spirit of compassion is well expressed in those lines, so often cited, which used to be sung at Mantua (in the 15th century still) in the Mass of St. Paul, relating how the apostle visited the poet’s grave at Naples and burst into tears, exclaiming, ‘What would I not have made thee had I found thee still alive, O greatest of the poets!’
In a footnote, he gives the Latin text:
Ad Maronis mausoleum
Ductus fudit super eum
Piae rorem lacrimae;
Quem te, inquit, reddidissem,
Si te vivum invenissem,
Poetarum maxime.
Rough translation:
Having been led to the tomb of Vergil he poured out the dew of a pious tear over him. ‘What I would have (re)made you, greatest of poets, if I had found you alive!’