 Complete the following phrase:  Tyrian purple may have been discovered as early as during the Minoan civilization. Alexander the Great, when giving imperial audiences as the Emperor of Macedonia; the Emperor of the Seleucid Empire; and the Kings of Ptolemaic Egypt all wore Tyrian purple. The imperial robes of Roman emperors were of Tyrian purple trimmed in metallic gold thread. The badge of office of a Roman Senator was a stripe of Tyrian purple on his white toga. Tyrian purple was continued in use by the Emperors of the Eastern Roman Empire until 