Tekhelet (Hebrew: תְּכֵלֶת təḵēleṯ; alternative spellings include tekheleth, t’chelet, techelet, and techeiles) is a “blue-violet”, “blue”, or “turquoise” dye prized by ancient Mediterranean civilizations. In the Hebrew Bible and in Jewish tradition, it was used on the high priest’s robes, tabernacle vestments, and the tzitzit (fringe) attached to the corners of quadrangular robes, including the tallit. Tekhelet is specifically mentioned in the third paragraph of the Shema, quoting Numbers 15:37-41. Neither the source nor the method for making tekhelet is given in the Bible. According to later rabbinic sources, it was composed solely of a sea creature known as a Ḥillazon. The knowledge of how to make tekhelet was lost in the Middle Ages, and since then tzitzit has contained no tekhelet. In modern times, however, many Jews believe that experts identified the Ḥillazon and rediscovered the tekhelet-making process, and now wear the tzitzit, which contains the resulting blue dye. The creature most commonly believed to have produced a true tekhelet is the slug Hexaplex trunculus (historically known as Murex trunculus). A tzitzit garment has four tassels, each with four cords. There are three opinions in rabbinic literature as to how many of the four strings should be colored with tekhelet: two strings; Chain ; or half rope.