destruction of the Second Temple, the identity of the source of the dye was lost, and since then Jews have only worn tzitzit without tekhelet. The Talmud mentions use of tekhelet in the period of Rav Ahai (5th-6th century); however the Tanhuma (8th century) laments that tekhelet has been lost. This loss appears to have been caused by a progression of historical events. Already in the first century, Caesar and Augustus restricted the use of the Murex dye to the governing class. Nero made laws that stated no one was allowed to wear purple because it was the color of royalty, and specifically he forbade goods dyed with Purpura (the name used for the Murex trunculus) under penalty of death. The idea that it was illegal to wear tekhelet is corroborated by a Talmudic story, in which rabbis caught smuggling tekhelet were liable to the death penalty. In the sixth century, Justinian put the tekhelet and argaman industries under a royal monopoly, causing independent dyers to cease their work and find other employment. The apparent final straw was the Muslim conquest of 639, in which the royal Byzantine dying industry was destroyed. Developments in the Jewish community may also have played a role, such as the proliferation of counterfeit (indigo) threads which made the procurement of genuine tekhelet difficult, and the persecution of Byzantine Jews which interfered with their export of tekhelet to Babylonia. Some have argued that the use of tekhelet persisted (at least in certain locations) for several centuries beyond the Muslim conquest, based on texts from the geonim and early rishonim which discuss the commandment in practical terms. The reason why royalty used the Murex dye as opposed to indigo which looked the same was because indigo faded. However once they figured out how to make indigo endure they stopped using the Murex trunculus because indigo was much cheaper. That time is when people stopped using the Murex trunculus for its Dye entirely. Identifying the color of tekhelet Despite the general agreement of the most of the modern English translations of the phrase, the term tekhelet itself presents several basic problems. First, it remains unclear to what extent the word in biblical times denoted a color or a source material, though it appears that at least in contemporary Mesopotamian sources, the cognate word takiltu referred to a color and not a material or dying process. Second, although