Melusine (French:[melyzin] may-loo-zeen) (or melusina) is a figure of European folklore, a feminine spirit of fresh water in a sacred spring or river. She is usually depicted as a woman who is a serpent or fish from the waist down (much like a mermaid). She is also sometimes illustrated with wings, two tails, or both. Her legends are especially connected with the northern and western areas of France, as well as the Low Countries. She is also connected with Cyprus, where the French Lusignan royal house that ruled the island from 1192 to 1489 claimed to be descended from Melusine.
[…] When in 963 A.D. Count Siegfried of the Ardennes (Sigefroi in French; Sigfrid in Luxembourgish) bought the feudal rights to the territory on which he founded his capital city of Luxembourg, his name became connected with the local version of Melusine. In 1997 Luxembourg issued a postage stamp commemorating this Melusina, with essentially the same magic gifts as the ancestress of the Lusignans. This Melusina magically made the Castle of Luxembourg on the Bock rock (the historical center point of Luxembourg City) appear the morning after their wedding. On her terms of marriage, she too required one day of absolute privacy each week. Alas, Sigfrid, as the Luxem-bourgish call him, “could not resist temptation, and on one of the forbidden days he spied on her in her bath and discovered her to be a mermaid. When he let out a surprised cry, Melusina caught sight of him, and her bath immediately sank into the solid rock, carrying her with it. Melusina surfaces briefly every seven years as a beautiful woman or as a serpent, holding a small golden key in her mouth. Whoever takes the key from her will set her free and may claim her as his bride.”
Sculpture by Serge Ecker