When you ask us to think about the Vergilian century you invite us to
accept the idea that interpretations of texts will change over time and
that changing historical/political frameworks (e.g. we are now post cold
war) will impinge upon how we read. My take on this is that when he writes
the prologue to Geo. 3 Vergil is thinking in similar ways. This
passage looks back to the Eclogues (esp. 4) and forward to the Aeneid;
in particular, scholars have concentrated on the ways in which it relates
to the Aeneid. Now this intensely literary, programmatic manifesto
is very self conscious about its generic status (it alludes to Homer,
Pindar, Calliamchus, Ennius...) and I would argue that one of the things
V. is thinking about is the reception of historical epic in the early 20s.
He begins by 'quoting' Ennius and ends by promising to write about the
pugnas Caesaris and the closing words are ab origine Caesar - but
the relationship between this projected epic and the actual Aeneid
is difficult exactly because Vergil is here dramatising the whole issue
of how a traditional Roman historical epic will mean something new after
Actium; ie it must confront Augustus. The many precise verbal connections
between the prologue and the shield in book 8 (they are all
in Buchheit, Anspruch) show that Vergil really is thinking seriously
about the whole question of literary tradition, reception and evolving
historical circumstances.
The text seems to encode viewpoints from different points in time. It can be read as a text which looks forward to a bleak future and the inevitable return of civil wars and the eventual fall of Rome (like Troy and Carthage), but it can also be read as a text which celebrates the end of civil war and the inauguration of a period of eternal sine fine peace. Because of the way Vergil is playing with time in the prologue to Geo. 3 (is it a Caesarean poem about the Trojan past or a Trojan poem about the Augustan future?) and in the Aeneid itself (eg all the temporal shifts in book 8), it is possible to look at Actium from the point of view say of both the mid 30s and the mid 20s. If one wants to argue for polyphony then this temporal aspect seems to me to be crucial.
The general lesson is that it will always depend where you stand in
time; are you a republican looking back or a Caesarean looking forward?
Augustus is trying to influence the ways in which people think about Roman
time; Vergil is thinking about this question in the Aeneid as he
deals with Roman time and history.