What shape was Utnapishtim's boat in the epic?

Utnapishtim's boat was a cube in the Epic of Gilgamesh.

In Tablet XI, the god Ea (Enki) warns Utnapishtim that the gods will send a devastating flood. He orders him to build a boat with equal length, width, and height, making it a cubical vessel rather than an ordinary ship. The boat is sealed with bitumen and loaded with Utnapishtim's family, craftsmen, possessions, and animals.

The unusual design is part of the story's mythic scale. The vessel has multiple decks and compartments, and its enormous dimensions emphasize that it is a divine rescue craft, not a historically practical river boat. Some modern summaries describe it as a “box” or “ark,” but those descriptions should not be mistaken for the text's geometry.

The flood lasts six days and six nights. After the waters subside, the boat comes to rest on Mount Nimush, and Utnapishtim releases a dove, a swallow, and a raven to test whether the land is dry. The gods later grant him and his wife immortality.