Although the ancient world could use all sorts of materials for dye including lime, ochre (petrified rust), soot, woad and even human urine, the most prized of all dye was derived from the murex, a crustacean whose bodily secretions contained high levels of iodine, producing a beautiful purple color. So prized and so difficult was it to extract murex dye that only the extremely rich could afford fully purple fabrics. This was the origin of the term porphyrygenitos or "born in the purple", which in Rome meant royalty — lesser men such as senators had to make do with purple colored trim in their clothing to denote their status.