This takes place in the seventh book.

The reason ascribed for the glaring improbability that the Greeks should have left their camp and fleet unfortified during nine years, in the midst of a hostile country, is a purely poetical one: 'So long as Achilles fought, the terror of his name sufficed to keep every foe at a distance.' The disasters consequent on his secession first led to the necessity of other means of protection.
Accordingly, in the battles previous to the eighth book, no allusion occurs to a rampart; in all those which follow it forms a prominent feature.

Here, then, in the anomaly as in the propriety of the Iliad, the destiny of Achilles, or rather this peculiar crisis of it, forms the pervading bond of connexion to the whole poem."-- Mure, vol.i., p.

257.
187 -- _What cause of fear,_ &c.
"Seest thou not this?
Or do we fear in vain Thy boasted thunders, and thy thoughtless reign ?" Dryden's Virgil, iv.

304.
188 -- _In exchange._ These lines are referred to by Theophilus, the Roman lawyer, iii.tit.xxiii.Section 1, as exhibiting the most ancient mention of barter.
189 "A similar bond of connexion, in the military details of the narrative, is the decree issued by Jupiter, at the commencement of the eighth book, against any further interference of the gods in the battles.