In "Sordello", how do we know the rejected spirit is Shelley?

Question

In book I of Sordello (1840) by Robert Browning, the speaker addresses a group of spirits,

Summoned together from the world’s four ends,
Dropped down from heaven or cast up from hell,
To hear the story I propose to tell.

But one spirit he rejects (pp. 3–4):

                stay—thou, spirit, come not near
Now—not this time desert thy cloudy place
To scare me, thus employed, with that pure face!
I need not fear this audience, I make free
With them, but then this is no place for thee!
The thunder-phrase of the Athenian, grown
Up out of memories of Marathon,
Would echo like his own sword’s griding screech
Braying a Persian shield,—the silver speech
Of Sidney’s self, the starry paladin,
Turn intense as a trumpet sounding in
The knights to tilt,—wert thou to hear!

In later editions of the poem (for example, the 1864 edition) Browning added the note “Shelley departing” to this passage, making it clear who is intended.

But in the first edition, which lacks the note, how were we intended to guess that the rejected spirit is the poet Shelley?

Answer 1

Browning gives us two, or maybe three, clues:

1. “The Athenian” is the Greek playwright Aeschylus, who fought the Persians at the battle of Marathon in 490 BCE. Shelley’s verse drama Prometheus Unbound (1820) takes the title of a lost play, attributed to Aeschylus, a sequel to the extant Prometheus Bound. (There is now some doubt over the authorship of Prometheus Bound, due to differences in vocabulary and theme from the more securely attributed plays of Aeschylus such as the Oresteia trilogy, but Browning in 1840 could not have anticipated this.)

2. The Elizabethan poet Philip Sidney is “starry” because of the pseudonym “Astrophil” (star-lover) he used for his sonnet sequence, and a “paladin” because he was a soldier, dying at the battle of Zutphen in 1586. Shelley’s essay ‘A Defence of Poetry’ (1821) takes its title and subject from Sidney’s The Defense of Poesy (1580).

3. “Thy cloudy place” perhaps alludes to Shelley’s poem ‘The Cloud’ (1820).

So Browning is referring to the fact that Shelley took models from Aeschylus and Sidney, and suggesting that he improved on them, making Aesychlus’s original verse seem “griding” (OED: “gride, v. To cut, scrape, or graze … with a strident, grating, or whizzing sound, or so as to cause intense rasping pain”), and Sidney’s elegant prose seem “intense as a trumpet”. Browning’s narrator fears that Shelley would do the same to Sordello, if he heard it. This is a kind of humblebrag—sure, Browning is saying, I may not be as good as Shelley, but I am in the same class as Aeschylus and Sidney!