Lost civilisation

It seems each province has its own lost civilisation. Morrowind has Dwemers, Hammerfell too, and Skyrim has also the Falmers. Cyrodiil has Ayleids and even Black Marsh has Kothringi. I don't know for Valenwood and Summerset. Don't you think Elsweyr should have one too? Not the Dwemers, of course, but the ruins of another civilisation which has coexisted or fought with Khajiiti? It could add depth to the background (and places to explore/loot).
At first I thought about Akaviri but it is written that there is only the Cloud Ruler Temple in Cyrodiil and the Tonenaka in Rimmen which are from akaviri architecture. And akaviri have mixed with imperials so they aren't really "lost".
Because beastfolks are said to be the first inhabitants of Tamriel, I've searched for lore and I've found this:

From Father of the Niben
We know that this strange, friendly feathered people the Pilot encounters will be lost - in fact, this poem is the only one where mention is made of the bird creatures of Cyrodiil. The literacy that Topal gives them is evidently not enough to save them from their eventual fate, likely at the hands of the "cat demons," who we may assume are ancient Khajiiti.

Topal never entered Elsweyr because he was afraid of the "cat demons". And when Aldmers came back centuries later in Cyrodiil, they found no evidence of the existence of bird-men. Maybe some sort of bird-men was in Elsweyr too. Maybe they "migrated" to Elsweyr and built a civilisation with the knowledge teached by Topal. And maybe their relation with Khajiiti was peacefull. Or maybe they became proud and arrogant and tried to enslave Khajiiti. There is a lot of possibilities.
In Indian mythology there is the Garuda, the bird-man, who is the ennemy of the Nagas, the snake-men. Maybe we could make our creatures exterminated by the Akaviri. That could explain also why the Akaviri was in Elsweyr.

I love you. I mean, yeah, I was hoping for a good excuse to have a lost civilization.

Great idea, grim. You seriously ought to be Head of Lore. No pressure, though. You can let another soul take up the title.

Too many emoticons? Never.

So what? Tree houses? Sounds fun.

Something that has two versions. Desert, and Foresty. At least. I'd think some above ground ruins would do them some good.

@Ryu: I would be honored to be Head of Lore. I promise not to be a tyrant about lore. And if so, fire me!

In Father of the Niben, bird-men look like parrots but I can't see parrots living in the desert. Maybe eagle-men? Or they evolved? Or there is two species? It something that match Elsweyr with its two environments. It looks like Shivering Isles with Mania and Dementia versions of people.
Entrance could be in height. They were birds after all. Player could have to jump or levitate to enter them.

I agree with the entrances idea. News for the front page...Head of Lore.

Idea of new lore:

And the Peacock King said: "All is right. Dreughs are in the Water, Khajiits are on the Ground and [name for Birdmen] are in the Sky." And in his great wisdom, the Mane agreed. But the Snakeman from the Other Side whispered: "How could it be right? Why the [Birdmen] build their nests and their palaces on the ground? Why don't they build them in the clouds?" Among those who heard him, some thought his words were poisoned, but most thought that he said the truth.

Two new characters:
The Peacock King is the ruler of the Birdmen. IRL, it's an asian deity, a peaceful Wisdom King who can protect from poisoning. In many asian legends, because of its plumage, a peacock is supposed to be the king of all birds.
The Snakeman is of course a Tsaesci. The Other Side obviously refers to Akavir. In lore, there are stories of Akaviri pirates early in the first Era so I think there could be a Tsaesci plotting in the Court of the Mane.

In hinduism, Garudas (Birdmen deities) are supposed to fight Nagas (Snakemen deities) so I make the war started by them.

It could explain many things:

• Why Khajiits don't like water: From this myth, it was the realm of dreugs. By tradition, they avoid water to not be attacked by them. (And of course, cats don't like to be wet )
  
• Why Birdmen and Khajiits was in war: Birdmen was the thieves of the Khajiit land. Khajiit don't care about concept like property but if they can access birdmen buildings, they certainly tried to break in. And maybe birdmen was arrogants because they can fly.
  
• Why Tsaesci was well considered in Elsweyr: They was not only beastmen but they also helped Khajiits to fight the birdmen. They probably imported knowledge and culture too.
  
• Why the Birdmen dissapeared: They was all hunted and killed by the Khajiits. When Versidue Shaie became Potentate in the 2nd Era, all Birdmen should be already dead. It's the end in the fight between the bird and the snake.

From Father of the Niben
There the Niben stayed for a moon, and the bird
Men learned how to speak their own words,
And with taloned feet, to write.

Topal the Pilot teached them how to write so you could use a derivative from Ehlnofex to create the signs. Words themselves can be all news.
Their language could be secret so the player have to search for understand it. This could be useful.

What would their architecture look like? Reminiscent of pyramids/ziggurats? Or something different? What if they literally built trees, or something like them? SO many possibilities.

Sadly, trees don't grow in the desert. Speaking about gameplay, dungeons will probably be underground or we'll have to build huge structures on the ground or to make interiors bigger than exteriors and explain it was made by magical means (like the TARDIS from Doctor Who? ) But it won't be very realistic.
It's not unusual for birds to live in holes in the rock. Look at the Roman Coliseum.

It's not the weather or the time which did most of the holes on it. They are all made by birds. So Imagine what could do an entire civilization of giant birds! But because they are intelligent, you could expect to find some sort of buildings for the entrances and some elements of architecture inside.

But what could build a winged civilization with clawed feet but no hands? Delicate sculptures and refined ornamentations will be physically difficult for them. We have to search something simpler. I think they could have buildings made of bricks. They can transport them easily and assemble them in heights. During the war with Khajiits, they could even be enough motivated to build fortresses too. But they need to be a lot. Their strength is in the number. Imagine thousands of birds carrying bricks through the sky! Each in turn, they lay their stone to build a monument!
Something like the Chachapoyas (the Cloud People) did in Peru.

For the stuff they made, we could have something organic decorated with feathers and what they found (skulls, wood, gems, etc...). I think they could ate something and regurgitated it to make a malleable material they used to make armors and weapons as dreughs do. They could also have great disposition for magic so you can use it to explain how they do some things.

We should avoid to use three different sets of models for the same "type" of architecture. The player have to be able to recognize it at the first sight. Birdmen architecture should be of one type as the dwemer and the daedric are. (Because I'm lazy too )
Making them living in trees means their dungeons will look like huge trees (probably with underground parts). It could be interesting for Pellitine but it's better to let this idea for the Valenwood province.

Not all the birdmen structures have to be in cliffs. They just have to be hard to access by walking. You could imagine them in craters or wells, a the top of a hill or of some rock. Some could have ways to access them but they should be narrow and tortuous.

I'm sorry if I didn't explain clearly. I wanted to make suggestions, but it seems that it does not look like.
I think birdmen could have a sort of peruvian-inspired architecture. You could have entrances of tombs, cities, temples and fortresses located in areas difficult to access. The same meshes could be used in desert and forest. In India, I found there is the same type of architecture in forest environment.
For the location of this ruins, imagine that they are like the dwemer ones but without bridges and narrow path to access them. Players will have to search to find them. Elsweyr don't have mountains but we could make canyons, cliffs and hills to put them.

And what about the birdmen themselves?
Are they all dead, like the dwemers, so you'll only meet ghosts of them?
Are they degenerated, like the falmers, so those you'll meet are more beasts than they was?
Are they hidden so the few you'll meet have their glory long gone?
A mix of all?

I realized it will be hard to make birdmen NPCs because of the wings. Birdmen as creatures it the only way we can do this. So yes, feral birdmen is a good idea. We could have several models for different class of birdmen like warrior, shaman/mage, unique characters, etc...
Westly have made some good models of birdmen. It's a shame that it has not yet shared them.

But maybe ours birdmen will look more like parrot (Pellitine version) or eagle (Ne-Quin'Al version). I'll try to make them from a modified Winged Twilight.

Take a look at the Gryphon Race by PhyntosWasp & Sabregirl
http://mw.modhistory.com/download--7066

The textures could use some updating, but it'd give you something to work with. According to the readme, it can be used as a resource:

"You may use and distribute the textures freely without additional permission as long as the above credits and contact information are included and they are distributed free of charge."

With some modifications, I think those could somewhat have a use here. Thanks for that, dawghaus.

They could have jewels too. Or some clothes as ornaments like belt, loincloth, crown or shawl. It's just something to show they was civilized.
I like the idea of colored feathers according to the magic they use. It's as if their magic could dye them. (Will white feathered birdmen be warriors because they never used magic? )We could even imagine an unique character with multi-colored feathers. He could be a sort of powerful wizard.
That could also explain why the ancient birdmen looked like parrots. They had a strong magic that is now lost. So it's why the actuals birdmen could be more dull.

Are the colors depending of the magic school they use or of the specific spell they have?

In the background, ancient birdmen could have mastered others (and lost) arcanes but with the actual engine we have sadly to stick with the classical magic system. Even scripted spells are hard to use with creatures.

This is what I think:
Purple for alteration: (Guard) I can see only Burden for it, with a good Shield spell. They are weak but hard to hit.
Blue for restoration: (Support) Fortify attribute. They could have healing spells too. You have to kill them quickly.
Red for destruction: (Shooter) I think Shock spells are the most suited. With a weakness to Shock too With ranged spells they'll be very annoying.
Green for illusion: (Assassin) Silence and Paralyze could make them lethal because the player couldn't hit. But if the player resists, they'll be defenseless.
White for mysticism: (Warrior) Absorb Health spell so the birdman will be stronger when the player will be weaker.
Yellow for conjuration: (Wise) It indicates that the birdman is intelligent because he can control a creature. But what sort of creature should they summon? A Daedra could mean they have a knowledge of Oblivion and its rules. A Undead could make them look like a sort of necromancer.

(We really should think about a name for the birdmen.)

From Father of the Niben
Brilliant flightful creatures of glorious colors
Greeted them in Aldmeri language,
Making the mer wonder, until they
Understood they were only calling back
The word they were speaking without
Understanding it, and then the sailors
Laughed.
Topal the Pilot was enchanted with the islands
And the feathered men who lived there.
There the Niben stayed for a moon, and the bird
Men learned how to speak their own words,
And with taloned feet, to write.
In joy for their new knowledge, they made Topal
Their lord, giving him their islands for the Gift.

It's the only reference to birdmen we have. We have supposed they had a link with Khajiits and that the isles they gave to Topal was something like a second home out of their main territory but there isn't more lore about them.