Plena Deo

Seneca the Elder, Suasoriae 3.5 ff., repeatedly attributes a phrase to Vergil which doesn't occur in any of the poet's surviving works--plena deo, literally "full of the god", with plena being nominative feminine singular. The phrase is equivalent to Greek ἔνθεος (entheos, whence English enthusiasm), and must have been used to describe a prophetess. In the Aeneid, two characters qualify, viz. Cassandra and the Sibyl.

Another Vergilian expression, tum vates, refers to these prophetesses:

- Aeneid 3.187: aut quem tum vates Cassandra moveret? (referring to Cassandra)
- Aeneid 6.582: tum vates sic orsa loqui (referring to the Sibyl)

In both passages, tum vates is metrically equivalent to plena deo in dactylic hexameter. Could tum vates have ousted plena deo in one or both passages?

Another possibility is that someone, after Vergil's death, completed one of the half-lines in the Aeneid with words including plena deo, and that such a version was current in Seneca the Elder's day. Aeneid 2.346 is a likely hemistich, as the context involves Cassandra.

In the case of both Cassandra and the Sibyl, the god who inspired them to prophecy was of course Apollo.