In “The Shield of Achilles,” Auden sets up stanzas that alternate between the past and the present as a way of taking a critical look at the modern world. The first, fourth, and seventh stanzas all begin:

She looked over his shoulder.

When Auden uses "she" and "his," he is referring to Thetis and her son Achilles, the great Greek hero/warrior. In each of these instances, Thetis is looking into the past. "Over his shoulder," she expects to see the beauty and culture of Ancient Greece engraved or reflected on Achilles's shield. For example, in the first stanza, Auden writes:

She looked over his shoulder
For vines and olive trees,
Marble well-governed cities
And ships upon untamed seas,

However, instead of the beautiful landscape and the interesting architecture, she has a prophetic vision of the present:

But there on the shining metal
His hands had put instead
An artificial wilderness
And a sky like lead.

The two longer stanzas that follow show a darker image of the modern world, one that is barren with faceless masses of soldiers, barbed wire, and empty justifications for war and violence. Auden makes an allusion to the crucifixion of Christ as a symbolic look to the darkness of the world that follows the Ancient Greeks.

In the final stanza, Auden looks to the past again:

The thin-lipped armorer,
Hephaestos, hobbled away,
Thetis of the shining breasts
Cried out in dismay
At what the god had wrought
To please her son, the strong
Iron-hearted man-slaying Achilles
Who would not live long.

Here, we see the heroes and gods of the past turning away and dying while Thetis cries out "at what the god had wrought." Here, Auden refers to the shield that Hephaestos has made for Achilles. This can also be seen as a way of looking toward the future from the past. The root of Greece's downfall was in the violence of Achilles all along, and it planted the seeds for the darker world of the present that was to come. This is why she always sees the future "on the shining metal" of his shield.