Oldest depiction of a merperson

The oldest depictions of fish-tailed mermaids and mermen occur in the art of ancient Mesopotamia. From the end of the 3rd millennium BCE through to the 7th century BCE, kulullû (fish-men) and kuliltu (fish-women) appear in glyptic art, in architectural decoration and as clay figures. The oldest surviving images are found on cylinder seals, which were used to imprint an image on a variety of media, such as administrative documents, baskets, doors and bags. Dating from the Old Babylonian period (c. 2004–1595 BCE), they can be found in museums across the world, including The British Museum, the Louvre and the Iraq Museum.

The visual cultures of ancient Mesopotamia undoubtedly had mermen and mermaids that predate the images that survive today, as attested by references to them in texts that predate extant depictions.

Featuring as monstrous opponents to hero-gods and protectors, the kulullû are found in architectural descriptions of temples and palaces and in ritual texts (where they had an apotropaic function protecting new buildings and their inhabitants). They are mentioned with other hybrid creatures like Bull-Man and Scorpion-Man, and sometimes alongside their female counterparts, the kuliltu or fish-woman. In the Babylonian Creation epic Enûma Eliš, the kulullû are birthed by the goddess Tiamat and defeated by the Babylonian god Marduk. A creature known as kulianna, a type of mermaid and perhaps one of the kuliltu, also appears in poetry of the late 3rd millennium as one of the "heroes" defeated by Ninurta/Ningirsu. Her body is draped on his chariot as a trophy.

In surviving glyptic art (seals and seal impressions) fish-men and possibly fish-women (though it is almost impossible to distinguish gender in many cases) appear in two forms from the end of the 3rd millennium BCE: either as fish with human heads and arms springing from their fish tails (these tend to be the earliest examples) or as creatures with the head, torso and arms of humans and the tail of a carp. In the oldest iconographical scenes in which they appear they are shown alongside the gods Enki/Ea (the water god), Utu/Shamash (the sun god), or Iškur/Hadad (the storm and rain god), often at their feet or as diminutive fillers around the devotional scenes which centre the gods. In such scenes it is likely that the fish-people have an astrological function as well as one of divine service. By the 7th century BCE the kulullû and kuliltu have taken on a greater role in ritual purification in glyptic art, often appearing in pairs as central figures flanking a sacred tree and holding sprinklers and buckets in the act of purification, Sometimes they are paired with the apkallū, or fish-cloaked sages. In such depictions, the distinction between fish-men and fish-women is easier to make as the figures are larger and more detailed.

Other early gods with fish tails include the Babylonian Oannes, who is credited with bringing knowledge and civilisation to mankind, and the Syrian goddess Atargatis, who usually appeared as a woman, but had the form of a mermaid in one of her avatars according to Lucian’s Dea Syria (2nd century CE). Atargatis is often mistakenly credited with being the first mermaid, but that accolade belongs to the kuliltu or the mythical being known as kulianna.