This is Blake’s illustration to part of Dante’s Inferno, from the Divine Comedy. It shows the trench of corrupt politicians in the eight circle of Hell. Above are the stone bridges that Dante describes as characteristic of this part of Hell, which was reserved for the fraudulent.
The half-submerged figures on the right are people who sold public offices; they are drowning in a sea of boiling pitch. Virgil and Dante are watching on the left, escorted by a group of devils.