Tyrian Purple (πορφύρα - porphúra) was an expensive dye used to manufacture ‘royal silk’ in the pre-Byzantine era: en.m.wikipedia.org/wiki/Tyrian_purple. For a long time, the silk was the most expensive man-made item by weight.
The use of the dye also goes back to ancient Phoenicians (also known as ‘land of the purple’).
Wonder if these scrolls have anything to do with royal trade?