Porphyry: the Royal (Purple) Marble

In Antiquity, purple was the colour of power and wealth, although both were mostly in the same hands. People went to extreme lengths (and costs) to acquire that colour.
[An imperial porphyry column in the Hagia Sophia]

A small sea snail, today known as the purple dye murex (Bolinus brandaris), produces a colourless secretion which turns into a brilliant puple dye when exposed to the air. To colour robes of dignitary purple you needed to harvest some 7,500 snails to obtain one gram of pure dye. This amount could colour just 15 cm3 of cloth. Imagine the costs of a robe for a king or high priest.

But, as always, purple clothes weren't enough to display your status. The most powerful even wanted their palaces built with the colour purple and that was a problem.

In 14 AD, a Roman legionary, discovered hard purple rocks in what is now the Gabal Abu Dukhan quarry in the Eastern Desert of Egypt near the Red Sea. Samples were promptly brought to the Emperor Tiberius in Rome. When Tiberius saw that this purple-coloured stone was solid enough for building and carving, he decreed that 'Imperial Porphyry' would be for the use of the Imperial family only. The term porphyry is from Ancient Greek porphyra (πορφύρα) and means 'purple'.

[Carmagnola, an imperial porphyry head in Venice] 

Tiberius quickly established a quarry on Mons Porphyry ('purple mountain') and began to use the stone for the decoration of Imperial palaces and other buildings. Later emperors continued the tradition. Imperial Porphyry was used for panels, floor tiles, statues, sarcophagi, and for the pillars of official buildings throughout the Roman world.

Perhaps most significant was the large circle of Imperial Porphyry in the centre of the floor of the Pantheon in Rome. For the next 300 years, new Emperors stood in this symbolic circle to be crowned.

This use to convey royalty made Imperial Porphyry truly the stone of Empire, causing it to be more significant, powerful and costly to the Empire than gold.

When the Emperor Constantine established Constantinople (now Istanbul) as the new Roman capital in 330 AD, he erected a 30-meter column of Imperial Porphyry with his statue at the top. The statue did not survive, but the pillar itself still stands. Eight Imperial Porphyry pillars also still support the niches of the Hagia Sophia, built by the Emperor Justinian.

In 600 AD the Byzantine Empire lost control of Egypt (and thus of the Imperial Porphyry quarry) to invading Muslim forces. Even its exact location was forgotten for centuries. The ancient quarry on Mons Porphyry was only rediscovered in 1823 by Sir John Wilkinson. It is now a World Heritage site.

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