In the Bible, the Israelites are commanded to have one of the threads of their tassels (') dyed with '; "so that they may look upon it, and remember all the commandments of the , and do them ()." corresponds to the colour of the divine revelation (Midrash Numbers Rabbah xv.). Sometime near the end of the Talmudic era (500–600 CE) the industry that produced this dye collapsed. It became more rare; over time, the Jewish community lost the tradition of which species of shellfish produced this dye. Since Jews were then unable to fulfil this commandment, they have since left their ' (' strings) white. However, in remembrance of the commandment to use the ' dye, it became common for Jews to have blue or purple stripes woven into the cloth of their '.