'Dwarf-coat, elf-cloak, blade of the downfallen West, and spy from the little rat-land of the Shire.'(RK 5.x.889)
So spoke the Mouth of Sauron, with all the relish of fresh insolence, meaning to daunt and dispirit Aragorn, Gandalf and the rest, to toy with them, just as Sauron his master meant to do (RK 5.x.888). Every attentive reader knows precisely to what and to whom he is referring here: the coat of mithril mail, the grey travelling cloak of Lórien, the blade from the barrow, and Frodo whom we last saw captured by the enemy (TT 4.x.742). Every reader also grasps the immediate allusion in the words 'blade of the downfallen West' to the long dead successor kingdoms of Arnor, but that participle 'downfallen' is more pointed and far-reaching than it first appears.
At the time of the publication of The Lord of the Rings only a few would have understood it. Even now its reference to Númenor itself, whose king and people Sauron had enticed -- nor were they all unwilling to follow -- to their destruction, can easily slip past us:
And even the name of that land perished, and Men spoke thereafter not of Elenna, nor of Andor the Gift that was taken away, nor of Númenórë on the confines of the world; but the exiles on the shores of the sea, if they turned towards the West in the desire of their hearts, spoke of Mar-nu-Falmar that was whelmed in the waves, Akallabêth the Downfallen, Atalantë in the Eldarin tongue.
No man of Gondor, no Dúnadan of the North, would have missed the point of this thrust, least of all Aragorn, its main target, who only moments earlier had received several more such barbs from the Mouth of Sauron:
'Is there anyone in this rout with the authority to treat with me?' he asked. 'Or indeed with the wit to understand me? Not thou at least!' he mocked, turning to Aragorn with scorn. 'It needs more to make a king than a piece of Elvish glass, or a rabble such as this. Why, any brigand of the hills can show as good a following.'(RK 5.x.888-89)
Given Aragorn's assertion of his kingship, his struggle with Sauron in the palantír (RK 5.ii.780), and Sauron's fear that he might have the Ring (5.ix.878-880), the heaped up insults, culminating in the reminder that Númenor, and its successor kingdoms, failed and fell, make perfect sense here. Even Gondor can field no more than a 'rout' and a 'rabble' more suited to a brigand than a king. But it was only Númenor that could defeat Sauron long ago, and Númenor lay downfallen beneath the waves.