How does the poem "The Shield of Achilles" contrast the Ancient and the Modern?

Auden takes the fundamental polarities found in Homer and
applies them to the modern setting.  The construction of the shield is meant to be a
very stoic and powerful image in the Ancient world.  When Thetis commissions Hephaestus
to make the shield, it is a moment that she believes will represent the glory of war. 
This represents the Classical view of war.  The demonstration of arete, glory on the
battlefield, and young men valiantly sacrificing themselves for the good of something
more noble and elevated.  Yet, the picture that Hephaestus renders on the shield is
representative of the modern reality of war.  There is hopelessness, images of a
distorted world, a rendering of plundering, rape, and violence present.  It is this
vision that Hephaestus creates that embodies the modern reality of war.  Auden is able
to capture this play between the ancient and modern in the construction of the shield. 
The reality is that Thetis' hopes represents the ancient and the shield's vision is the
modern.  Once Hephaestus leaves, the battle is suspended in terms of which vision will
become accurate.  In the end, Auden rightly draws out that with Achilles' death, the
barren depictions of the shield in terms of waht war's reality is turns out to be more
accurate.  It is here where Auden's Modernism is present in a Classical
context.