Rock art in Ravenna, Italy

In August, on our way back north from Gubbio, we stopped at Ravenna, a small city famous for its 5–6th century Byzantine mosaics. Ravenna is just 2 hours south of Venice and is well worth a 2–3 day visit. The purpose of this post is two-fold. (1) To introduce readers to a place with incredible interior art work mostly made with small to large pieces of rock. (2) To explain the origin and importance of Imperial (purple) porphyry.

In the earliest 5th century, as the Western Roman Empire was weakening, Emperor Honorius transferred the capital from Rome to Ravenna, where it remained until Ravenna was conquered by the Ostrogoths and their king Theodoric in the late 5th century. In the 6th century, the Eastern Roman Empire expelled the Goths and came to power under the Byzantine Emperor Justinian. During these periods, rulers expended vast resources to build and decorate the interiors of their churches and monuments. Eight locations in Ravenna, all with magnificent early Christian art, have been designated as UNESCO World Heritage Sites.

The mosaic art

The Basilica of Saint Vitale is the major masterpiece of Byzantine art in Ravenna. It was completed by Emperor Justinian in the 6th century using elements of both Roman and Byzantine architecture. It is a UNESCO site on every visitor’s “must see” list.
Every surface of the basilica’s interior is covered by art, from the inlaid rock floor, to the columns and walls, and up into the dome. It’s hard to imagine how many person-hours went into this art project. Notice how pieces of marble rock are arranged in the wall panels to create interesting patterns. The mosaic heads on the archway include Christ and his 12 disciples. The dome is painted, but everything else is mosaics or decorative rock panels.
As was the custom at that time, most of the art has a religious theme. In this mosaic, a beardless Christ sits on a blue globe representing the universe. He is offering Saint Vitale (for whom the basilica is named) the crown of martyrdom while Bishop Ecclesius is offering Christ a model of the church. Angels appear to be overseeing the proceedings! Lots of gold was used in this mosaic.
There are also political themes—unsurprisingly, given that funding came from the emperors’ caches. This life-size mosaic in the Basilica of Saint Vitale shows Emperor Justinian in a purple robe and golden halo, flanked by Archbishop Maximianus and priests on his left and soldiers on his right. This combination indicates Justinian’s position as leader of both Church and State, and the halo gives him a Christ-like appearance.
This mosaic is from the Archbishop’s museum (Chapel of Saint Andrew), created when the Ostrogoths were in charge of Ravenna. I’m not sure what this strange creature is doing, but with the more close-up view, it’s possible to see the individual mosaic pieces called tesserae. Tesserae are small cubes of rock, ceramic or glass that are carefully cut and pieced together to make the intricate designs. The process requires a great deal of time and skill, as shown in this YouTube video:

Imperial Porphyry

Purple porphyry is found in some of the art work in Ravenna. It was a hallmark of royalty and power during the Roman Empire and remains a highly valuable rock today.

The name “porphyry” is derived from the location where this rock type was found. In 18 AD, a Roman Legionnaire discovered a beautiful purple rock in Mons Porphyrites (Porphyry Mountain), a remote part of the eastern desert of Egypt. It has a deep purple background color with larger white crystals. This porphyry quickly became the most prestigious stone of Rome and Byzantium. It was reserved exclusively for the Imperial court of the Roman Empire—hence the name “Imperial Porphyry”. Contributing to its value is porphyry’s durability and hardness, properties that require a highly-skilled artisan. If you do an internet search for “Imperial Porphyry”, you will find some spectacular examples of busts, vases, containers and other art works from that period. You will also find that this rock continues to bring extravagant prices.

Despite the inaccessible, harsh location in the Egyptian desert, the Romans quarried this treasured stone until the late 5th century, when the quarry was abandoned. It was rediscovered in the 1800s, but remains a place that is very hard to get to, and very hard to quarry.

Here is a piece of the purple porphyry rock from Mons Porphyrites. To me, the most interesting thing is that geologists now use the word “porphyry” to refer to any volcanic igneous rock with larger crystals in a very fine-grained ground-mass. The two crystal sizes are a result of magma (liquid rock) rising up and then erupting at Earth’s surface. The larger specks are feldspar minerals that crystallized underground before the volcano erupted. The dark-colored ground-mass consists of very small-sized crystals of a variety of minerals that crystallized after the volcano erupted. While underground, magma cools slowly and crystals have time to grow large. But when erupted onto Earth’s surface, magma—called lava once erupted—cools quickly and crystals have insufficient time to grow large.

The porphyritic rock found in Mons Porphyrites is just one example of what is now a whole geologic category of rocks called porphyries. They are typically silica-rich volcanic rocks that were erupted explosively from stratovolcanoes. Although Italy was not the source of Imperial Porphyry, it is well known today for its variety of other porphyritic volcanic rocks. Many are mined to sell as decorative paving stones or other uses that require an attractive, durable material. Here’s an example of a high-quality porphyry product from the province of Trentino:

Your assignment!

I could have posted many images from the UNESCO World Heritage sites in Ravenna. But they are better seen in person, so put Ravenna on your northeastern Italy “must see” list. And keep a lookout for purple (imperial) porphyry. I’ve seen it in museums in the United States, and scattered about in many parts of Europe. Because it was so valuable, it got stolen, recycled, and otherwise redistributed since it was quarried in the 1st-5th centuries. The best place to see it is in Rome, particularly in the Vatican. Of course, you should look for regular porphyry too. It is abundant on continents and when you see it, you will know that volcanoes erupted there!

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  1. Jolene on September 30, 2022 at 5:41 pm

    Very very interesting! The artwork in the basilica of Saint Vitale is stunning. The rock art is amazing as well. Thanks for sharing.

    • Landscapes Revealed on September 30, 2022 at 5:44 pm

      Thanks Jolene! I’ll have to show you more photos of the artwork.

  2. Kathleen Myers on October 1, 2022 at 8:58 am

    Are your trips open to folks?
    Kathleen Myers

    • Landscapes Revealed on October 1, 2022 at 4:13 pm

      Hi Kathleen, Because I am not a tour company, I don’t have the ability to arrange logistics for groups. My goal is to share geologic information about places I visit with others who are interested in these locations. Thanks for your interest!

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