Commentary on line 3
The simile is copied by Virgil, Aen. x. 264 sqq.
Quales sub nubibus atris
Strymoniae dant signa grues, atque aethera tranant
Cum sonitu, fugiuntque notos clamore secundo.
Cf. also vi. 311, Juvenal xiii. 167. ou)rano/ei pro/, before the face of heaven. πρό goes with the locative instead of the gen. in two other phrases, 8.561 Ἰλιόθι πρό, 11.50 ἠῶθι πρό. H. G. 225.
