What purple was and what it meant, however, continued to be contested and debated. In the fourth century, clothes dyed with genuine Tyrian sea‐purple – purple diadem, all‐purple silk robe, purple trousers, purple shoes – became formal imperial insignia, and their replication or imitation by would‐be usurpers was rigorously policed. By the beginning of the fourth century, Lactantius was able to state that a purple‐dyed garment was for the Romans now a badge of royal distinction. Royal purple (regia purpura and porphurē basilikē) became regular tags in political jargon, and purpura was frequently used as shorthand for imperial authority: purpuram sumere (to take on the position of emperor), natales purpurae (the date commemmorating the anniversary of the investiture of the emperor's purple robe), and diuina purpura (marking imperial affinity to the divine). The emperor and his heirs were born and died 'in the purple' – born in a porphyry‐walled chamber (Porphyrogenitus) and buried in a porphyry sarcophagus. The Roman eye was trained politically, philosophically and linguistically to connect this colour with the body of the emperor. Sea‐purple workshops along the Phoenician coast became imperial property, and the ritual of 'adoratio purpurae' started to gain currency in the imperial court. Adoratio was a ritualised and institutionalised show of allegiance in which the loyal subject would kneel down and kiss the corner of the emperor's purple robe. Pliny, remembering the robe's fishy origins, might have seen the irony, but for Roman intellectuals of the later Empire, purple had developed a new definition as the imperial colour: its new 'object' – one might argue – was not the purple snail but the figure of the emperor.
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