Resurrection rosette

Flower between the Tyches of Palmyra and Dura Europos, the froniter post on Rome's eastern border. From the fresco of Julius Terentius performing a sacrifice.
Here is the whole:
Wall Painting of Julius Terentius Performing a Sacrifice Paint on Plaster, H. 107.0 cm, W. 165.0 cm From the Temple of Bel, Dura-Europos, ca. 239 CE Yale University Art Gallery, Yale-French Excavations at Dura-Europos: 1931.386 Photography © 2011 Yale University Art Gallery
The most recent, scholarly view (with which I concur) is that the tribune of the Palmyrene XX Cohort is leading his men in making sacrifice (of incense) to the trinity of emperors (upper left) ruling in 238 CE. Two, good sources on this:
The image is, in general, now well-understood. However, although everyone sees the flower, it is not described, so I will attempt this here.

First, the flower appears to be a dogwood (Comus)*.

Cultural references
A Christian legend of unknown origin proclaims that the cross used to crucify Jesus was constructed of dogwood.[24] As the story goes, during the time of Jesus, the dogwood was larger and stronger than it is today and was the largest tree in the area of Jerusalem. After His Crucifixion, Jesus changed the plant to its current form: He shortened it and twisted its branches to assure an end to its use for the construction of crosses.[25] He also transformed its inflorescence into a representation of the Crucifixion itself, with the four white bracts cross-shaped representing the four corners of the Cross, each bearing a rusty indentation as of a nail, the red stamens of the flower representing Jesus' Crown of Thorns, and the clustered red fruit representing His Blood.[26][27]
24. The Old Legend of the Dogwood
25. Jeffrey G. Meyer (2004). The Tree Book: A Practical Guide to Selecting and Maintaining the Best Trees for Your Yard and Garden. Simon and Schuster. pp. 258–. ISBN 978-0-7432-4974-4.
26. Thomas E. Barden (1991). Virginia Folk Legends. University of Virginia Press. pp. 61–. ISBN 978-0-8139-1335-3.
27. Ronald L. Baker (1 August 1984). Hoosier Folk Legends. Indiana University Press. pp. 7–. ISBN 0-253-20334-1.

Here, we see how the pagan mythology as at Dura Europos is later adopted - as so often - by Christianity.

We see such a floral emblem on Herodian tombs:

This Levantine rosette has a long history, much older than the Herodians.

"Seal impressions from the Jemdet Nasr period (ca. 3100–2900 BCE) show a fixed sequence of city symbols including those of Ur, Larsa, Zabalam, Urum, Arina, and probably Kesh. It is likely that this list reflects the report of contributions to Inanna at Uruk from cities supporting her cult. A large number of similar sealings were found from the slightly later Early Dynastic I phase at Ur, in a slightly different order, combined with the rosette symbol of Inanna, that were definitely used for this purpose. They had been used to lock storerooms to preserve materials set aside for her cult. Inanna's primary temple of worship was the Eanna, located in Uruk (c.f. Worship)."

One version of the star symbol of Inanna/Ishtar
"As a symbol, the rosette is often thought to evoke the goddess Inanna/Ishtar. Given its pervasiveness in Neo-Assyrian iconography, especially in association with figures of the genii and the king, there may be a more universal symbolism behind the motif, such as regeneration, rebirth, or initiation, all of which may after all be thought of to be encompassed by Inanna/Ishtar's religious symbolism in ancient Mesopotamia."
- The Mythology of Kingship in Neo-Assyrian Art by Mehmet-Ali AtaƧ, Cambridge University Press, 2010

The petals are often illustrated as heart-shaped, which allows the four to be seen as eight. This symbol, usually termed a rosette, is very ancient indeed and is seen from India, across the Middle East, to Egypt. It is a solar symbol (and the source of the ancient swastika).
On 29 July 238, Pupienus and Balbinus were killed by the Praetorian Guard and Gordian proclaimed sole emperor; the three had ruled together for three months. Maybe the sacrifice offered by these soldiers at Dura Europos was to mark the deaths of these emperors and their expected resurrection.

*Thanks to Lisa Hansley for helping with the identification.

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