The poem is preceded by a Latin epigraph from Juvenal: “Quis ineptae [iniquae] / Tam patiens urbis, tam ferreus ut teneat se?” (Juv. 1.30-1). Roughly translated, the lines mean: “Who can so endure the wicked city or be so iron-willed as to bear it?” The epigraph establishes that the poet has been moved to write his satire because of the follies of the city. Only an “iron-willed” person could see the city’s vices and not react. The epigraph foreshadows the poem’s righteously indignant tone at the corrupt, disordered world its two characters inhabit.

18th-century poets like Johnson perfected the heroic couplet—sets of rhyming lines written in iambic pentameter. “London” is an illustrative example. Written entirely in heroic couplets with an AABBCC rhyme scheme, this long work has fairly regular line lengths and few enjambments. Its uniform structure lends itself to the classical form Johnson is using, with pithy rhymes bringing out the sharp satire. The poem has a declamatory quality; it is meant as a public address to a targeted audience of English people. Johnson emphasizes the oratorial aspect by filtering the poem through two characters.