The Jonah Sarcophagus: Detail, Jonah is thrown from the ship

Jonah goes nude into the maw of the sea monster, as catechumens do when they enter the baptismal pool (Senn, 94; Jensen, "Nudity," 310-11). It is not clear why the sailors are also nude.

Detail from an ancient Corinthian vase: Perseus slays the sea monster, which is labeled ketos. (Source: Wikimedia Commons.)

The monster has the forked tail of a whale but the twisty body of a serpent. In the Greek of Matthew 12:40, Jesus calls it a ketos. This can be translated "whale" and indeed gives us the scientific name for the whale order Cetacea, but it is also used just to refer to any sort of sea monster. An ancient Corinthian vase, for example, pictures Perseus slaying the sea monster, which it labels ketos. The Septuagint also uses ketos in translating Jonah into Greek. The Hebrew term really means "great fish," and that is how the Vulgate renders it, but this sarcophagus antedates the Vulgate and presumably relies on the Greek in giving the monster in this image a whale-like tail and a monster-like serpentine body.

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Photographed at the Museo Pio Cristiano by Richard Stracke, shared under Attribution-NonCommercial-ShareAlike license.