Was looking at the portrait of the tetrarchs, and other Eastern Roman/ Byzantine sculptures and works of art. They look so much more rugged and simple (of course this is not necessarily a bad thing) . . . By no means am I making the silly claim that it was a “downgrade”, it’s just interesting how dramatic of a change it was. Edit: architecture looked so much different too. Was this because of Western Roman influence? In contrast, Western Roman sculptures look more similar to those of Classical Greece. For example, compare the portrait of Gordian III to that of the portrait of Constantine.
In Art History classes I've heard some professors write this stylistic change off as "a descent into a darkened / unenlightened age", but that always feels too simplistic when you look at these pieces on the full timeline of art periods.
There were a number of influences that may have shaped this stylistic shift, from internal conflicts, invasions and natural disasters... the theory would be that society was no longer producing and nurturing these geniuses that understood anatomy, subtle visual planes, etc and making/ copying (most of our surviving examples of Greek sculpture are Roman copies - the Romans mostly added examples of portraiture to the Classical style) the statuary seen in that Classical Greek period.
The reality was that there was a style after the Classical period that even made those idealized figures look artificial. This was the Hellenistic period, where the goal was realism and all the wrinkles, figure flaws and other idiosyncrasies that went with the highest representation of reality. These statues looked like real people and the Roman's also painted to be incredibly life-like. One example is the Old Drunk Woman. I almost wonder if this combination was the first occurrence of what we now refer to as "the uncanny valley". There is something about near perfection in replicating humans that can be quite disturbing. This shift may have been influenced by a return to the more symbolic depiction of humans as used in the past, and aways from this slightly disturbing realism.
Also, just speaking culturally, the ideas of people were changing. The Greeks equated beauty with truth - art and architecture were meant to reflect this soundness of mind through the measured, predictable compositions of buildings and sculptures. The Romans followed the Greek style, adding innovations like domes, reinforcements, etc... until they suddenly didn't. It's as if they got bored and started making these buildings with hybrids of Greek, Egyptian and entirely new elements. The Late Empire art was marked by a return to the stylized line - away from purely realistic representation. The eyes in portraiture are enlarged - no longer a photographic representation, but more like the votive statues of the past... this symbolic, wide-eyed look communicates abstract ideas about the individual, whereas their realistic depictions may not (large eyes suggest things like the sitter being "all seeing", intelligent... it's also linked with heightened spirituality).
Is the height if realism truly artistic perfection? If so, then the Impressionists and Expressionists were essentially undermining the Renaissance influences... (many DID think Impressionist art was trash in their lifetimes). But the reality is that they helped us see things with more than our eyes - they evoked feeling. The "fall" from Classical Greek to Late Empire was just a development in style and the mentalities that dictated what was valuable (artistically speaking). This is a shift from realism to abstraction that happens back and forth throughout art history.
I'm not entirely sure why you're characterising 4th century Roman art as "Byzantine", nor why you'd compare it specifically to that of classical Greece 800 years earlier. The portrait of the Tetrarchs, to take your example, pre-dates the founding of Constantinople and we're not sure where it stood before it was placed there. For all we know it was Western Roman.
But you're quite right to note that a fairly drastic change in artistic style took place in the Roman empire somewhere between the 2nd and 4th century A.D.
Unfortunately this is not my area of expertise so I can't answer your question. But fortunately, the question has been asked and answered in the past by u/Anthemius_Augustus who has some wonderful links (only some of which are broken...) and explanations.
I imagine you'll find the examples of 10th century "classical" style Byzantine art quite interesting, as I did when I first read that post.
Just as a Re: to the edit from /u/OutsideSpring. The Romans were pretty good at identifying assets from other cultures and incorporating the pieces they liked into their own. Later on, there were architectural influences from places like Egypt, Persia, etc. There were also earthquakes, which may have altered the "city-scape" and objectives of future buildings. There was economic hardship in the Western Empire that meant a shift of talented craftsmen away from that area (but like the US in the 18th century, this influx of talent would benefit another location, not simply vanish). Cement was also a new building material that would impact the way building were constructed - which in turn altered their overall appearance, as compared to building with marble, as they did in periods prior. Maybe some or all of these elements are playing into what you observe?
They still utilized their architectural breakthrough, the arch, and developed that into the vault, making massive amounts of space, charged with this ethereal visual impact inside the buildings (so maybe not as impactful from the exterior). They were light-years ahead of the Greek architecture they emulated in terms of engineering.
As far as the portrait of Gordion III versus Constantine... Gordion III's is definitely made in a more hyper-realistic (and potentially heavily idealized, hardening back to old days of stabilty and "classical values") style. This was around the time when 26 soldier emperors claimed and lost their reign in rapid succession. They were only in power for months to a year each. The sense of instability during those years must have been... overwhelming. As a comparison, here is a portrait of one of those solder-emperors, Trajan Decius (249-250), looking very realistic - and absolutely overwhelmed by anxiety. Trajan with deeply lined brow and anxious expression
There is another statue of another soldier-emperor, Trobonianus Gallus, again "idealized", in a heroic pose as was more typical of the "Classical Greek" period... but the man's torso is MASSIVE. Trobonianus with classical pose and exaggerated body. This is exaggeration that will later come into play in Constantine's portrait. The bulk is to emphasize the "large and in charge", overwhelming presence of the emperor. Henry VII of England did a similar "propaganda" portrait, where he was just made to appear... enormous. Again, probably trying to instill a sense of lasting impact, using earmarks from the past to connect himself to the 'good old days' and secure his image and reign.
When you look at the work of the Ancient Egyptians, the blocky, rigid figured seem more like they are made of stone than the open, airy, almost toucbably soft marble renderings of the Ancient Greeks. The Egyptians were concerned with eternity - and being eternal is felt when you look at their sculptures. This same blocky look is seen in the Tetrarchs' portraits carved in porphyry - perhaps this was a grasping at stability and lasting cohesion... when the previous years where chaotic and uncertain.
I think the Late Roman Empire was frought with conflicts within and without and even environmental and that is reflected in their aesthetic shift. Maybe you just see the crack in their facade (pun intended). 😉
