By which river did the gods swear their oaths?

The Styx is the river by which the gods swore their oaths in ancient mythology. In Greek myth, the Styx is a primordial river that forms the boundary between Earth and the Underworld. It is often associated with various themes of oaths and promises, where the gods would make solemn vows upon its waters. An oath taken on the Styx was considered to be irrevocable, and breaking such an oath would result in severe consequences, reflecting the river's power and sanctity.

The other rivers mentioned do not have the same significance in terms of oaths. The Amazon, while a real river, holds no mythological context in this regard. The Nile is crucial in Egyptian mythology but is not associated with the swearing of oaths among the gods. Lethe, another river from the Underworld, embodies forgetfulness and the waters of forgetfulness rather than the solemnity of promises. Thus, the Styx stands out as the definitive river associated with divine oath-taking in mythology.