If in ancient mythology, a mermaid is a creature half-woman half-bird, in the medieval bestiaries, she is described as half-woman half-fish. Here we find the influence of the Scandinavian tradition, where the mermaid is a sea monster called "margygr", meaning the giant of the sea.
It is only from the fifteenth century that the mermaids will be represented as a beautiful creature with long hair.
Usually, they symbolize the souls of the dead. They are known for their captivating vocals, charming fishermen in order to lead to certain death. Thus, in Homer's Odyssey, Ulysses asks his crew to fill their ears with wax so as not to hear, while he remains attached to the mast of their boat.