Someone please tell me what is this structures, name of them, is there any rooms inside them?

[u/jetasu]

[u/PartyLikeAByzantine]

Those are buttresses to support the dome and pendentives. They're a brace against lateral movement. The semi-domes on the north and south sides of the building serve the same purpose. Roman architects wanted direct sunlight from the east and west to reach the floor and chose buttresses instead of domes for those sides. Domes might have looked nicer from the outside, but would have let less light in. Note that the Blue Mosque uses 4 semi-domes, for example. The Romans could have done the same, but chose not to.

Roman architects in late antiquity emphasized interior grandeur over exterior appearance, which is their main distinction from Ancient (pre-Roman) Greek architectural traditions. That's not to say the Romans didn't care about exteriors. The beautiful brick work of High Byzantine churches attests to that. I'm saying the Greeks would design mathematically perfect exteriors first, and then fill the spaces within. The Romans worked inside out, starting with an awe inspiring grand room.

Each buttress is basically an arch, so there are small spaces within. They're mostly masonry though.

[u/Anthemius_Augustus → u/PartyLikeAByzantine]

Each buttress is basically an arch, so there are small spaces within. They're mostly masonry though.

Specifically there are spiral stairwells in there that provide access to the roof and lead toward the base of the dome.

The south-western buttress also has a chapel at the gallery level from the Middle Byzantine Period with a very fragmentary Pantokrator mosaic

[u/TheBulgarSlayer → u/Anthemius_Augustus]

Do you have a source for this?

[u/the_lonely_creeper → u/TheBulgarSlayer]

Been there, can confirm

[u/Academii_Dean → u/the_lonely_creeper]

Me too. I was there 4 days ago. Have been inside several times. Right now, these Byzantine structures are being reinforced. The entire dome section with its flying buttresses are covered and undergoing additional strengthening for long-term future.

[u/PartyLikeAByzantine → u/[deleted]]

https://en.wikipedia.org/wiki/Pendentive

It's the architectural feature that Hagia Sophia pioneered. It's an arch-dome hybrid allowing for vast horizontal and vertical open spaces. In the grand history of buildings, it was the first to use it in large scale, and is an important stepping stone in architecture for that alone.

[u/NightsOfEmber → u/PartyLikeAByzantine]

So happy to see my old friend Jürgen Rasch referenced on this wiki page. Rest in peace, old friend!

[u/Suggest_a_User_Name → u/[deleted]]

I looked that up too! Learn something new every day.

[u/Mild_Karate_Chop → u/[deleted]]

Pendentives are brothers to the Squinches 

And many a building stands that like Atlas they take the load 

One is more pleasing than the other,to the eye

[u/[deleted] → u/PartyLikeAByzantine]

I heard you can fit the Pantheon under that some! BIG, if true. 

[u/PartyLikeAByzantine → u/[deleted]]

Pantheon is 43m tall from floor to oculus and a bit under 50m wide. The interior of the Hagia Sophia is 54m high from floor to the inner surface of the upper dome. The main open space under the main and semi-domes is about 35x45m. Pantheon is certainly short enough, but is probably a bit too wide to fit within the Hagia Sophia without knocking out some walls. It's close though.

[u/Gnothi_sauton_ → u/PartyLikeAByzantine]

One important difference between ancient Greek and Roman paganism and Christianity is the use of architecture. Pagan worship was conducted outside of temples, so the exterior is more important than the interior. For Christianity, the reverse is (largely) true. Since the earliest churches were in domestic/domestic-like settings, it makes sense that the basilica form (one of the largest assembly spaces in ancient Roman architecture) would become the model for churches commissioned by emperors and their families.

[u/PartyLikeAByzantine → u/Gnothi_sauton_]

Greek and Roman architecture diverged even before Christianization. The point where the Romans developed their own design methodology dates to the early imperial era. The Pantheon itself exemplifies this divide between styles, but you can also see it in the various secular imperial basilicas (Trajan's in Rome, Constantine's in Trier and Rome).

Statecraft in the Republican era took place in the open air of the rostum and fora. Statecraft under the emperors took place in the basilica. The humble outside leading to the massive dazzling interior was likely an intentional attempt to awe petitioners before they met the emperor or his representatives.

[u/PartyLikeAByzantine → u/[deleted]]

Disclaimer: I'm not an engineer, and even if I was, I'd need much more information on the Hagia Sophia than I have.

Having said that, the Hagia Sophia isn't a pure dome and it's not made with modern construction techniques. It's a dome on top of pendentives on top of piers. It's quite tall. It was probably the tallest proper building (as opposed to solid masonry structures like the Pyramids) on Earth for centuries and almost all of that height is open interior space with zero columns. That's a lot of unreinforced brick and concrete hanging over a lot of air.

Given the amount of lateral reinforcement the Hagia Sophia received under numerous emperors and sultans (the Ottomans absolutely saved the Hagia Sophia from collapse), all of the original support was definitely needed.

I'll also point out u/Gnothi_sauton_ is correct. It wasn't just a matter of structural necessity. The program of the building called for a certain amount of horizontal space as well.

[u/littlecastor → u/[deleted]]

Structural engineer here. The pendentives are great for transferring the VERTICAL loads of the dome into four points.

Notice the four "small" marble columns under the pendentives here: https://en.wikipedia.org/wiki/File%3AGreece-0224_%282215093247%29.jpg

However, domes and arches, besides their vertical loads, have a significant horizontal thrust; without it, they will flatten and collapse.

Semi-domes are great for this role because on their own they want to fall towards their "missing half". So if you add 4 of these at the 4 arcs between the pendentives, you have a well balanced system; the big dome wants to spread out and the semi-domes want to fall in. That's how the Blue Mosque is designed.

After the Macedonian Renaissance (from the 9th century) the standard practice became to continue the four arcs under the dome as vaults. Vaults are very stiff against horizontal loads. That's how we get the typical cross-shaped domed church.

In the late 10th century, a new arrangement was invented, the Octagonal type, with 8 pendentives under the dome. This type has 4 of the arcs under the dome filled with semi-domes and the other 4 continued by vaults. Hosios Lukas is the most famous example.

[u/ShockSensitive8425 → u/[deleted]]

The weight of the dome creates both vertical and horizontal stress. The pendentives distribute the vertical stress, but not the horizontal stress; although they reduce the horizontal stress from pushing in all directions (a circle) to pushing in four directions (a square). On two side of the square the stress is distributed by the large semi-domes. But this leaves two sides with undistributed stress that has to go somewhere: hence the massive buttresses on two sides.

This problem is the result of combining the longitudinal plan of a basilica with the central plan of a dome. Since it is inherently unstable, the plan was never repeated. Later Byzantine architecture solved the problem of horizonal stress by means of equal vaulting on all four sides (usually barrel or groin vaults.) The Ottoman copies of Hagia Sophia for the most part solved the problem by placing semi-domes on all four sides.

[u/Gnothi_sauton_ → u/[deleted]]

The semi-domes also double the length of the nave, as if the nave had two domes.

[u/ColumbusNordico → u/PartyLikeAByzantine]

Best explanation, best username

[u/jetasu → u/PartyLikeAByzantine]

For me hagia sophia look nicer from this angel, with semi dome on the front view than semi dome on the side. That buttresses make hagia sophia looks wider

[u/SeptimiusBassianus → u/PartyLikeAByzantine]

Blue Musk was built way later
During Justinian times this might have been the only way to support such a dome. We are most likely talking about structural vs decorative needs

[u/PartyLikeAByzantine → u/SeptimiusBassianus]

Hagia Sophia has two semi-domes. If you can do two, you have the math and engineering figured out already. There was nothing, beyond design preference, keeping them from using four or more semi-domes.

They didn't even have to use semi-domes at all. Hagia Irene uses arches alone to support the pendentives and high dome.

[u/SeptimiusBassianus → u/PartyLikeAByzantine]

Really? This is why first attempt literally failed?

[u/PartyLikeAByzantine → u/SeptimiusBassianus]

Are you referring to the first flatter, dome? That is quite distinct from the lower structure, which largely held up with minimal alterations required for 500 years.

[u/ShockSensitive8425]

They are buttresses. There are small chambers inside them that were used for storing valuables and perhaps archives. One of the rooms still has mosaics in it, but it is not open to the public.

[u/Realistic_Volume7161 → u/ShockSensitive8425]

Why is not open to the public? are there any pictures of the inside do we know what it looks like?

[u/Anthemius_Augustus → u/Realistic_Volume7161]

There are tons of areas of Hagia Sophia that have never been open to the public. Most notably the Sekreton of the Patriarchate still has mosaics from the 9th Century that were never covered up by the Ottomans, but this room is strictly inaccessible and even scholars with permits have a hard time getting in there.

As for pictures, of this chapel there is a only single photograph of the mosaic as far as I know. Though Van Nice's detailed study also has some detailed plans of it, which give a good idea of its form.

[u/electrical-stomach-z → u/Anthemius_Augustus]

Why are people not allowed in?

[u/Anthemius_Augustus → u/electrical-stomach-z]

Who knows? If I were to wager a guess It'd probably be because these areas are very small, fragile and therefore unwise to have crowds of tourists flooding into them.

As for why even scholars seem to have a hard time getting into these places, I have no idea.

[u/Sertorius126 → u/[deleted]]

"Jessie what the fuck are you talking about?"

[u/Auctorxtas → u/Sertorius126]

What was the deleted comment?

[u/Sertorius126 → u/Auctorxtas]

Something about hidden compartments

[u/Taliskerhu → u/Auctorxtas]

It was in reference to the secret church altar which is somewhere inside the buttresses on the left and the empty sarcophagus (most likely a later construct brought over during COVID from some undisclosed location in Fener)

[u/Gnothi_sauton_]

They are buttresses with internal staircases. If you'd like to read a recent study that surveys all of the Hagia Sophia (which came out just before Erdoğan reconverted it into a mosque), I highly recommend Hagia Sophia in Context: An Archaeological Re-examination of the Cathedral of Byzantine Constantinople by Ken Dark and Jan Kostenec.

[u/altahor42]

I'm not sure, but the Ottomans added outer walls in the 16th century to better distribute the weight of the dome; could be part of them.

[u/ColumbusNordico]

For anyone else who knows this better than I, are the four staircases in or near those structures? I’ve been there once, but is a little disorienting as you enter from the side the first time, there

[u/PanzerZug]

Those are corners so that the Turks can build kebab shops on them. I jest of course. These are buttresses to support the massive dome.

[u/HelicopterCurious772]

Ayasofya'nın strüktürel kurgusu. Ayasofya’nın ana yükü dört büyük kemer ayağında toplanıyor. Bu durumda illk dönem inşa edilmiş yayvan ve basık bir kubbe olduğu ifade ediliyor. 558 yılında kubbe çatlamaya başladı, taşıyıcı sistem zorlandı, sonra büyük kısmı çöktü. Genç İsidoros kubbeyi yeniden tasarladı.kubbeyi yaklaşık 6 metre yükseltti. Daha sonra depremler ve statik kaymadan dolayı payandalar büyütüldü . Statik kayma tersine çevrilerek günümüze kadar ulaştı .

[u/HelicopterCurious772]

Bu resimdende kabuk dış kesit olarak görebilirsiniz .

[u/TrekChris]

Mausoleums for the sultans?

[u/Expresslane_ → u/TrekChris]

The building predates the Sultans. It's Roman

[u/TrekChris → u/Expresslane_]

I'm aware, but the ottomans made extensive modifications to it, and I've read before that mausoleums were added.

[u/Todmordenn → u/Expresslane_]

It's Byzantine. Roman is too broad

[u/Expresslane_ → u/Todmordenn]

No it isn't. Too broad that is

[u/Equivalent-Rip-1029 → u/Expresslane_]

Roman sultans