Classical culture was presumed to be the origin of the "civilized" culture of the Victorians; therefore, the reimplementation of classical themes works to reaffirm this metanarrative, to establish continuity with a coherent linear past. Which is different from the self-conscious bricolage of architectural styles in postmodern architecture, which serves to dismantle and confuse narratives either as a critique or as a free play of jouissance, liberated from any kind of idea of continual progress.
perhaps, but "modern" consciousness begins with a sense of separation from the ancient past, i.e., the renaissance project was aimed at recovering as much of the classical past as could be done -- which meant very little
i.e., the byzantines had a sense of "continuity" with the classical past, even though there was in fact great change and were countless mutations over the years -- how could there not be? 1000 years from fall of rome to fall of constantinople -- nearly 2000 years from plato to circa 1400/1500
(byzantine emigre scholars in northern italy sparked the renaissance in the west, as it happens)
the modern as such takes the shape of a "quarrel" against the ancients -- i.e., modern learning and techniques as superior to that of the ancients
so in political philosophy, at a very early date, there's machiavelli -- but the first full-on mdoern political philosopher is hobbes -- machiavelli and hobbes reject aristotle's teaching and promulgate a more realistic, (allegedly) more effective teaching
and then i suppose descartes is the first modern for straight philosphy
or whatever. i'm not a school teacher. the point is that victorians, as moderns, did not have a sense of continuity with the classical past. they may have been schooled in the classics, but such schooling could not bridge the chasm of 1000+ years. certainly matthew arnold knew that the classical and especially christian forms were dead
as for the postmodern, i think it is the consciousness of despair -- i.e., the despairing recognition that nothing can be done to improve man's lot absolutely -- i.e., that there is no fully satisfactory political solution -- that things are indeed a zero-sum game
and in science, i guess the postmodern begins with the notion of paradigm shifts, i.e., that although a fundamental way of approaching/understanding nature may yield great insights and knowledge, that same approach will close-off other questions and kinds of knowledge