Mentre rinova pur l'ampia cittade
L'arme contra i nemici e le difese,
Vaga colomba per cerulee strade
Vista è passar sovra il signor francese,
Che non dimena i presti vanni, e rade
Quelle liquide vie con l'ali tese;
E già la messaggiera peregrina
Da l'alte nubi a la città s'inchina.
While the great city (*) keeps renewing its
Weapons and defenses against the enemies,
A beautiful (**) dove across light blue roads
Is observed passing over the French lord; (***)
It doesn't flap its swift feathers but touches
The yielding element with wings wide open; (****)
And already the traveling messenger
From the high clouds glides towards the city.
(**) Vaga is a basically untranslatable poetical adjective that conveys the idea, at the same time, of something beautiful and wandering, especially across the sky. It referred typically to birds and stars. The same ambivalence had peregrina, see line 7, that meant either/both "pilgrim" or/and "rare, precious, wonderful." Here it has been rendered with "traveling."
(***) Godfrey of Bouillon
(****) Imagery coming from Virgil, Aeneid 5; it had already been reused by Dante in Inferno 5: 82-84.