The Girdle of Melian was the name for the invisible boundary set by the 'sorcery' of Melian. She set this boundary around the kingdom of Doriath to protect Thingol's lands from anyone entering without the king's express permission.

The Girdle was first set shortly before the beginning of the First Age, and within it were all the lands of Doriath, including the forests of Neldoreth and Region and the wood of Nivrim.

The Girdle was removed when at last Melian departed Middle-earth after the death of Thingol.
Encyclopedia entry originally written by atalante_star