The Amarantin were a species of bird-like aliens whose planet, Resurgam, was rendered lifeless by the Inhibitors 990,000 years before humanity resettled it. Their written language was stereoscopic, requiring humans to merge the text in their visual cortex before it became readable. They were also intensely social creatures, with isolation from their flock causing severe psychological repercussions.
Despite possessing wings, Amarantin could not fly. This featured heavily in the mythology, which claimed that their god -- Birdmaker -- traded them their intelligence for their flight; a pact that, if broken, would be rescinded.
Sometime thousands of years before the Inhibitor attack, the Birdmaker's edict was ignored by a group of experimentalists, led by an Amarantin called Sun Stealer. They experimented first with optics and mirrors, which was the cause of the leader's name, and then with mechanical flight. The latter caused them to be ostracised by their fellows, fearful of tampering with the pact supposedly made eons before. Eventually they became the Banished, and left Amarantin society -- and finally the planet itself.
Thousands of years later, they returned. Technologically advanced enough to possess nanotechnology, they were hailed as new gods, and monuments were constructed in their honour. Ironically, shortly after abandoning Birdmaker en masse, the Inhibitors fulfilled his pact and wiped out the Amarantin on Resurgam; only the remnants of the Banished survived, hiding in the Shrouds.