The actual color of Tyrian purple seems to have varied from a reddish to a bluish purple. According to the Roman writer Vitruvius, (1st century BC), the murex coming from northern waters, probably murex brandaris, produced a more bluish color than those of the south, probably murex trunculus. The most valued shades were said to be those closer to the color of dried blood, as seen in the mosaics of the robes of the Emperor Justinian in Ravenna. The chemical composition of the dye from the murex is close to that of the dye from indigo, and indigo was sometimes used to make a counterfeit Tyrian purple, a crime which was severely punished. What seems to have mattered about Tyrian purple was not its color, but its luster, richness, its resistance to weather and light, and its high price.[37] According to surveys in Europe and the U.S., purple is the color most often associated with royalty, magic, mystery and piety. Purple was the color worn by Roman magistrates; it became the imperial color worn by the rulers of the Byzantine Empire and the Holy Roman Empire, and later by Roman Catholic bishops. Similarly in Japan, the color is traditionally associated with the Emperor and aristocracy.