All through Dante's inferno we see different types of sinners being punished according to the crimes they committed on earth. In the Seventh Ring, Dante and Virgil face the violent and in their journey they first encounter the violent against their neighbors. After facing the minotaur a centaur escorts them along side the river of blood where tyrants and murderers face their punishment. Here me see poetic justice being served to the criminals depending on the severity of their crime. Tyrants such as Alexander, who killed so many men, lay deep inside the river of blood with only his eye brows being exposed. Others, who's crimes weren't as severe have more of their bodies protruding from the river, and as Dante walks more and more the sinners have more of their bodies exposed.
Poetic justice consists of vice being punished and virtue rewarded, not just this circle is a perfect example but the Inferno as a whole is just that precisely. Sinners lay deep in the realm of evil suffering from the worst punishments (vice being punished), no innocent soul is in the inferno except for Dante who is just visiting. In the following books when they visit heaven we see the other half of poetic justice being served, when virtue is there rewarded. Poetic justice was key in Dante's masterpiece as we could clearly see in the 7th circle as well as the rest of Inferno.
