By what river did the gods swear?

The river by which the gods swore is the Styx. In ancient Greek mythology, the Styx is a significant river that separates the world of the living from the Underworld. It is often depicted as a place of great power, and oaths taken by the gods upon this river were considered unbreakable. When Greek gods made promises or oaths, they would place their trust in the Styx, ensuring that their commitments were solemn and binding. This deep-rooted connection to the Styx emphasizes its importance not only in divine matters but also in the beliefs surrounding death and the afterlife.

In contrast, the other rivers listed have different mythological associations. Lethe is known as the river of forgetfulness, where souls drink to forget their earthly lives; Phlegethon is associated with fire and is one of the rivers of the Underworld; and Acheron is often referred to as the river of pain, linked to the passage of souls into the underworld. While each of these rivers holds importance in mythological contexts, none of them share the same significance in terms of divine oaths as the Styx does.