"An Arundel Tomb" uses alliteration fairly regularly throughout its seven stanzas. Oftentimes, this takes the form of sibilance. The first example comes immediately in the poem:
Side by side, their faces blurred,
The two /s/ sounds form a pair, and the pairing of sounds is used throughout the poem ("plainness" and "pre-baroque" in line 7, "his left-hand" in line 9, etc.). Of course, sound-pairs are a way that the poem can gently hint at the poem's main pair: the earl and countess, who have been paired together for a number of centuries by this point (in life, death, and stone). The /s/ sounds are themselves "side by side."
The next key example comes in stanza 2. In fact, there are two important uses of alliteration one after another:
... a sharp tender shock,
His hand withdrawn, holding her hand.
The /sh/ sounds have a sort of tenderness and sharpness to them all at once, and, in being used for the first time in the poem, might come as a surprise on the reader's ear—mirroring the speaker's surprise at noticing the way in which the earl and countess are depicted holding hands. The /h/ sound—the first letter of "hand," of course—then dominates the following line, showing the permanence of the earl and countess's pose cast in stone. The /h/ grips the line, mimicking the action of holding hands.
Later, the alliteration of the /t/ sound in lines 37 to 38 underscores the thematic connection between the stone effigies, the passage of time, and truth itself:
Time has transfigured them into
Untruth. The stone fidelity
This connection is bolstered by the consonance of "into" and "fidelity." Altogether, the insistence on the /t/ sound here suggests the inevitability of "truth" or intention changing over time—even for objects made of stone.