Achilles is the Greek hero and the protagonist of Homer's military epic the "Iliad." Homer chronicles in great detail and in a grand manner the heroic deeds of Achilles during the Trojan war. During the course of the war, Achilles had lost his armour after lending it to his dearest friend Patroclus who was killed in the war by Hector. Achilles' mother Thetis asks the blacksmith of the gods, Hephaestus to make new armour for Achilles. The new shield which Hephaestus made for Achilles is described in great detail by Homer in Book 18, lines 478-608 of the "Iliad." It is a classic example of an 'ekphrasis' or 'ecphrasis,' that is, a dramatic and vivid description of a visual art. Homer describes vividly the images which decorate the shield in nine concentric circles or layers. There are various interpretations to the images found on the shield, but what is central to the images is the all comprehensive variety, vitality and fecundity of human life in general.
Auden's "The Shield of Achilles" (1953) is his direct 'modern' response to Homer's description of Achilles' shield. The numerical symbolism of the nine layers or concentric circles of Homer's Achilles' shield is mirrored in W.H.Auden's poem which has nine stanzas.To quote from the refernce link of enotes:
"Stanzas 1, 4, 7, and 9 are set squarely in ancient Greece, and the reader’s gaze is directed toward Thetis and Hephaestos. These stanzas are composed of eight three-stress lines; the second and fourth lines rhyme, as do the sixth and eighth. The other stanzas, in which the scenes of modern life are presented in detail, are quite different. These stanzas are in the seven-line form known as rime royal. The lines are in iambic pentameter, with the rhyme scheme ababbcc. The contrast is striking, both visually and aurally, and it is impossible not to notice the movement between stanzas focused on Thetis’s innocent expectations and those focused on the harsh realities depicted on the shield."
In Homer's "Iliad" war although destructive had a certain grandeur and larger than life appeal. On the contrary, Auden's three (a platoon of soldiers going out to battle, three men being executed, and "a ragged urchin aimless and alone") images cynically describe the meaninglessness and futility of modern day warfare and life in general "where promises were [not] kept."
"Out of the air a voice without a face
Proved by statistics that some cause was just
In tones as dry and level as the place:
No one was cheered and nothing was discussed;
Column by column in a cloud of dust
They marched away enduring a belief
Whose logic brought them, somewhere else, to grief."