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As a child I'd often play in the Labyrinth at Hawara, tie one end of the skein of thread to the entrance, if ever I got lost I'd follow it until I found my way back out. It has been enchanted by the Witches of Caucus. The thread will not tangle or break.
~ Ariadne on giving Jason the thread.[src]

The Skein of Thread was an enchanted thread that belonged to Ariadne. It was attached to a necklace and would never tangle or break.

It was originally enchanted by the Witches of Caucus. Ariadne gave the skein to Jason in order for him to find his way into the Labyrinth and out again. Jason tied one end to the cave entrance and was able to travel through the caves without getting lost. He returned the thread back to Ariadne and he was grateful for it. (The Earth Bull)