Purple, the so-called royal dye, was the most beautiful and expensive dye in antiquity. It was known in Minoan Crete and on the Aegean islands and because of its importance it has been thoroughly described by almost all writers of the time. Here, in this article we have concentrated on the famous purple of Hermione which for over 1000 years was the most prized in the East. First the technology of the times is described and then we go on to examine the dye chemically, phasmatoscopically and macroscopically. Purple dye came from the shell murex of the district. Purple gave to the fabrics of the time an impressive and peculiar violet hue, similar to that of an amethyst. The colour difference between Hermione purple and its rival Tyros purple is also recorded in this article. These were the two prevalent royal purple dyes in Mediterranean countries. The Hermionian purple was found at Susa by Alexander the Great and described by Plutarch.