In the opening of Dante Alighieri’s epic poem Divina Commedia, or Divine Comedy, Dante strays from what he calls the true path—the true way to salvation—and finds himself alone in "a gloomy wood" (canto 1), a wild, impenetrable forest.
Dante sees a mountain ahead with a bright light shining above it, but his way to the top of the mountain is blocked by a lion, a leopard, and a she-wolf, which symbolize, respectively, lust, pride, and greed.
From this dark and forbidding forest of what might be considered original sins, Dante must travel down into the further darkness of Inferno (Hell), then up through the mottled light and darkness of Purgatorio (Purgatory), before he can reach the top of the mountain and the eternal light of God in Paradiso (Heaven).
Symbolically, mankind is born into darkness—into sin—and struggles to find its way into the light of salvation and ultimately into the presence of God.
We begin as creatures of darkness, and we spend our lives seeking to become creatures of light. Some of us fail utterly, succumb to a life of sin, and are thrown into the eternal darkness of Hell. Others of us have yet to find our way to the light when we die, and we must reside in Purgatory for a time until we're purged of the lesser sins that keep us from reaching he light. Some of us reach the eternal light of God on our own merits, or after a time spent in Purgatory where our sins are washed away.
As Dante travels down into Inferno, the atmosphere itself is described as being "air browned with shadows" (canto 2), "air pierc'd by no star," and "air with solid darkness stain'd" (Canto 3). God's light doesn't penetrate into Hell. The air itself is darkness.
Dante encounters sinners and their punishment in different environments of darkness. Dante arrives in the Second Circle of Hell where the lustful are punished by gale-force winds and torrential rains in the "black air" (canto 5).
Into a place I came
Where light was silent all. (canto 5)
The bodies of water in Hell are equally devoid of light.
Far murkier was the wave
Than sablest grain: and we in company
Of the' inky waters, journeying by their side,
Enter'd, though by a different track, beneath.
Into a lake, the Stygian nam'd, expands
The dismal stream... (canto 7)
The black waters of the stream, lakes, and rivers in Hell represents the darkness of sin, and contain all of the sins committed by those in Hell, as well as all of the sins that have been washed away in Purgatory.