Aviontix is designed to be an "ancient kingdon" to be plopped into a game world as history. However, you can make it a current game world, if you want.
Aviontix is templated off the Egyptians, with a different slant, so bare with me.
The key ideas:
The lands of Aviontix are mostly desert now, with several small rivers running through it. At the time of the Kingdom, it was naturally greener and lusher. This was enhanced by waterworks allowing canals, and irrigation. However, these massive waterworks have fallen to the weight of time since then.
Long ago they build great cities, and monuments, and water works. The Aviontix never seemed to do anything on a small scale. That is why so much of their society (via ruins) has survivied to the modern era.
Where once there was a thriving urban peoples, there are just nomadic herders, who are expert riders. The only link to the Aviontix, is that they are known far and wide as the best hunting bird tamers. Every male of age has one (if not more). Some people whisper of magic that allows them to be bound to their birds. They even call the land Aviansis, (wings of sand… referencing the wind).
In the land of Aviontix there are ruins. A lot of ruins. There are many sand buried cities, king’s tombs, and huge statuary. However, Aviontix was a kingdom so long ago, that everything has been looted. (Figure there has been a whole historical epoc or two since then) There might be a hidden tomb or something somewhere in the lands, but it is unlikely. This does not stop people from selling maps to them all the time.
They were the first humans to develop magic without the assistance of an elder race (like elves). They laid down the basics of magic still used today by Human peoples. They also created the sciences of mathematics, architecture, agriculture, and the written word.
Nothing comes directly from them. Their language has been lost of the sands of time, but many ancient texts reference their works as foundations.
They were a very religious people, focused upon their leaving to the afterlife. They associated magical spirits/ gods with birds. It is difficult to determine if this was metaphorical or actual. Their gods are shows as fully human, human with a bird head, or as large birds. In fact, the names for their Gods have become the "common name" for most birds.
Given their beliefs, bird motiffs are everywhere among Aviontix artifacts and ruins. If you find a really old magic item, it will have a bird motiff on it… given that it came from Aviontix. While Aviontix was a very magical place, very few of their items have survivied the "sands of time". Many have been broken, but most are lost or unable to be recharged.
In addition, it seems that Rocs (huge birds) and Pheonixi/ Firebirds were either created by or bred to their present form, by the Aviontix.
Additional Ideas (2)
The Hawkstar: A hero that keeps coming back to undo Evil done by man in the world. He is a warrior that uses ancient weapons and can summon a pair of wings (if desired). Current manifestation has him fighting a corrupt theocracy....
Master Destini is one of the world mages, those who are responsible for sheparding the world. Destini is an Avatar of Divine Order. Destini became this avatar twelve centuries ago when he became the wielder of The Destiny Helm (Sort of a stylized Hawk's Beak, and flaring tops... more gryphon than bird). This artifact is the actual Avatar, granting the ability to perceive order and chaos, and shift wild chaos towards order and unyeilding order towards a gentle randomness.
Fate's Tower: Almost not a material location. Only those who have have a heroic destiny (Will be heroes, are heroes, or are heroes that have lost their way) can actually find it with any regularity. (It is impossible to see from the sky) It is a forty by forty foot square tower about 90 feet tall, with castly like ramparts at the top. There is no door, and only one window about 75 feet up. You will find it impossible to climb or enter it without permission from Destini.
Golvek: A master work golem that could ascend to Godhood if it wanted to. It was created to mimic any skill, power, or ability that came within 100 feet of it. It was designed to be the ultimate creation, then used in a bit of fury as an ultimate weapon. Golvek is now trying to determine its place in the universe.
Dove and Hawk: These spirits guide pairs who must maintain the balance between the violence and peace to maintain order. Those so endowed gain great strength and durrability.
The Raven: This one does not appear as a bird based villian/ hero. However, the god sends out avatars from time to time to create death and chaos for him to feed off of. Currently the Raven is a high Bishop in the Corrupted Theocracy, only a few steps from the HighOne.
This is another early mostly human society. It was Stone, moving into the Bronze, age society. As with all early societies, it was harnessed under the yoke of religion, with temples being the central unifying focus. They built in adobe and clay, with only a minimum of stone. That is why few of their temples or cities survive.
The Sarethian's deities were serpentine in nature, as the Aviontix were avian. It was not an Evil Society, as most people assume snake worshipers are. It was a mixed back of good, kind of good, and kind of selfish dieties. There are more records of Sarethian society, as their written language formed the earliest foundation of written modern Human languages. That is not to say there is a lot of records, just some. Very little survives of their culture except for a few scrolls of exceptional poetry and magical theories, and their entire legal system (which was draconic at best - mercy not being a big quality for the Sarethians).
If one pays attention to those records, Sarethians were said to have immense healing powers and to have healthy long lives associated with it. They had skills in mind and illusion magics, but little else. Most of what they had was meditation based, with a few things stolen from the Aviontix.