Subitis umbris, not, as Heyne thinks, the sudden return of darkness, which would be inconsistent with the appearance of a dream as distinguished from a vision, but simply the sudden apparition, the plural being used of a single phantom, as in 5. 81, G. 4. 501 (where I incline to retract the explanation given in the note).
 For ‘stimulat’ I have restored ‘instimulat’ from fragm. Vat., Pal., Gud., &c., as the less common word, and so more likely to be corrupted. ‘Sancte deorum’ is an imitation of Ennius (A. 1. fr. 46), “Respondit Iuno Saturnia, sancta dearum,” which is itself an imitation of δῖα θεάων. An ordinary partitive genitive individualizes some members of a class in order to distinguish them from others: here there is individualization where apparently no division is intended.
 There is no reason to suppose that Aeneas had any doubt that it was Mercury whom he had seen, as we are expressly told that the Mercury of the dream was in all respects like the real god. The case is even stronger in 9. 22, where Turnus, having first addressed Iris by name, afterwards says, “Sequor omina tanta, Quisquis in arma vocas;” though there, as possibly here, the doubt may be about the god who had sent down the messenger. But it seems to have been usual to throw in a saving clause, from motives of reverence, in case the speaker should have mistaken the god or addressed him by a name unacceptable to him. Serv. says that the pontiffs were accustomed to pray “Iuppiter omnipotens, vel quo alio nomine appellari volueris,” exactly the Ζεὺς ὅστις ποτ᾽ ἐστίν of Aesch. Ag. 160.: comp. 9. 201, and see further Serv. on 2. 351, Gell. 2. 28. Possibly there may be something in another suggestion of Serv. that the doubt is expressed in consequence of the number of gods bearing the same name, e. g. three Mercuries are spoken of. Heyne, who censures the “argutiae” of Serv. and others, can hardly be said to have explained the matter by reminding us that Aeneas only saw the form of Mercury, and had no guarantee for its reality. ‘Iterum’ refers back to ‘iterum instimulat.’ Some MSS. however give ‘inperioque tuo.’ ‘Paremus ovantes’ 3. 189.
 “Ἵληθι, ἄναξ, ἵληθι φαανθείς,” Apoll. R. 2. 693. “Placidi servate pios” 3. 266. ‘Sidera,’ apparently from the connexion of the stars with the weather, above v. 309, G. 1. 311 &c. Aeneas then prays that favourable weather may be sent for his voyage. ‘Caelo,’ in or over the sky.
 Repeated from 3. 208.
[584-629] ‘At dawn Dido looks forth and sees the fleet sailing off. She breaks out into wild rage—asks whether none will give chase—wishes she had torn him and his limb from limb while they were in her power—prays that if he must land in Italy, he may land only to be involved in war, and may perish miserably, and that there may be everlasting hostility between Carthage and Troy.’