Servius, Commentary 1.108:

[Explaining the line, Tris Notus abreptas in saxa latentia torquet, ‘Notus twists three ships snatched up onto the hidden rocks.’]

Hidden rocks: They are hidden only because of the storm, not (as some assert) when the sea is calm. For, how can rocks which have received a name be hidden? In any event, these rocks lie between Africa, Siciliy, Sardinia, and Italy. The Italians call them ‘altars’ because there the Africans and the Romans entered upon a compact and wished their boundaries to lie there. For this reason, Dido says, ‘I call upon shores contrary to shores, waves contrary to waves.’ These altars are called ‘propitious’ by Sisenna. Other people say that the Greeks have called these rocks bomous (altars). Some people say that this spot was once an island, which suddenly went to the ground, and its remains are extant in the form of these rocks, on which they say that Phoenician priests used to conduct their religious rites. Others call these the altars of Neptune, as for example Claudius Quadrigarius in the first book of his annals, who has ‘among the altars, which were called the altars of Neptune.’ Varro, says of the shore in his first book, ‘As these people do, who head to Sicily from Sardinia or vice versa. For if they have lost sight of either of these islands, they know that they are sailing dangerously and they fear the island lying hidden in the sea, which they refer to as the altars.’

saxa latentia modo propter tempestatem, non ut quidam tradunt tranquillo mari; nam quemadmodum latent quae nomen habent? haec autem saxa inter Africam, Siciliam et Sardiniam et Italiam sunt, quae saxa ob hoc Itali aras vocant, quod ibi Afri et Romani foedus inierunt et fines imperii sui illic esse voluerunt. unde et Dido “litora litoribus contraria, fluctibus undas inprecor” . quae arae a Sisenna “propitiae” vocantur. alii dicunt Graecos haec saxa βωμοὺς appellare. quidam insulam fuisse hunc locum tradunt, quae subito pessum ierit, cuius reliquias saxa haec exstare, in quibus aiunt Poenorum sacerdotes rem divinam facere solitos. has aras alii Neptunias vocant, sicut Claudius Quadrigarius I. annalium “apud aras, quae vocabantur Neptuniae” . Varro de ora maritima lib. I “ut faciunt hi, qui ab Sardinia Siciliam aut contra petunt. nam si utramque ex conspectu amiserunt, sciunt periculose se navigare ac verentur in pelago latentem insulam, quem locum vocant aras” .