Servius, Commentary on the Aeneid 4.228:
“She did not save him from Greek arms twice for that reason… (Aeneid 4.228)
Some say that ‘twice’ here was once, in his single combat with Diomedes, in which Aeneas was struck by a boulder which Diomedes threw. Juvenal has, ‘or with the mass by which Diomedes struck Aeneas’ hip’. And similarly, in the destruction scene, we read ‘I descend, and with a god leading me…’ and ‘this was my sweet mother.’
Others say that it is ‘twice’ because of the single combats of Diomedes and Achilles. But when he fought with Achilles, he was saved by Neptune. This can, nevertheless, be seen as stemming from Venus’ influence, for Juno this imputes the action to her, saying, ‘…and you were able to turn the nymphs into as many fleets.’ There can also be another sense: for Troy was once captured by Hercules, who was Greek, and we can understand that Aeneas was already alive at that time. Nor did much time pass before (as everyone agrees) power was handed over by Hercules to Priam.”
graivmque ideo bis vindicat armis alii dicunt ‘bis’ semel a Diomedis singulari certamine, in quo a Diomede percussus est saxo: Iuvenalis “vel quo Tydides percussit pondere coxam Aeneae” : et item in excidio, sicut legimus “descendo ac ducente deo” et “hoc erat alma parens”. alii dicunt propter Diomedis et Achillis certamina singularia. sed quando cum Achille dimicavit, a Neptuno liberatus est: potest tamen hoc pro Venere factum videri: sic enim Iuno imputat Veneri quod pro ea factum est dicens “et potes in totidem classes convertere nymphas”. potest etiam et alter sensus esse: nam Troia antea ab Hercule, qui et ipse Graecus fuit, capta est: ut intellegamus iam tunc Aeneam natum fuisse: nec enim multum tempus interfuit, cum constet Priamo tunc ab Hercule imperium traditum.