I wander thro' each charter'd street,
Near where the chartered Thames does flow.
And mark in every face I meet
Marks of weakness, marks of woe.
In every cry of every man,
In every Infant's cry of fear,
In every voice: in every ban,
The mind-forged manacles I hear.
How the Chimney-sweeper's cry
Every blackning church appalls;
And the hapless Soldier's sigh
Runs in blood down Palace walls.
But most thro' midnight streets I hear
How the youthful Harlot's curse
This line, along with  the one immediately after it,  refers to the way events are controlled by outside forces. The “hapless” soldier’s sigh “run[ning] in blood” down the enclosures of power–metaphorically staining the palace’s pristine walls–could speak to Blake’s understanding of the futility of existence, the destructive stupidity of war, or the fact that soldiers who die while following orders have literally given control of their life to their country, and thus lack agency over their fates. 
 Note the  alliterative  repetition of ‘a’s and 'p’s in 'appalls’ and ‘hapless’, which give unity to the stanza.  Also the  plosive  ‘b’s and 'p’s in 'blackening’ and ‘blood’, and ‘Palace’, ‘appalls’ and again ‘hapless’ express the anger and despair of the speaker. The sibilant ’s’s imitate the sound of sighing. 
 To reinforce the speaker’s  synaesthesia  — whose  ‘mind-forged manacles’  sees the worst in everything around him (an unfortunate condition of Experience) and causes him to have his aural experience manifest itself in horrible sights (literally seeing sounds) — Blake has made an acrostic of this stanza with the first letter of each line spelling ‘H E A R’. The speaker is overwhelmed by the suffering that marks his perception as much as it marks the hapless victims of an Industrial Empire. 
 Although  Blake had an encounter with a drunken soldier invading his property  in 1803, who is named in Blake’s later prophetic works (and a reversed image from this plate of the old man and child appear in Plate 84 of ‘Jerusalem’), our sympathy here in London is with the soldier as a victim of the state. 
 There is also irony in the returned Soldier who sheds blood to protect a system that keeps him in such terrible conditions, so he is indeed ‘hapless’. Simon Armitage arguably provides a contemporary echo of this soldier’s sigh in the poem  Remains .
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