the Imperium is designed to be "the Ancient Empire whos "golden age" all others aspire to" inserted into a game world as history.

In the land of Aviontix there are ruins. A lot of ruins. There are many sand buried cities, king's tombs (They were a very religious people, focused upon their leaving to the afterlife), and huge statuary. However, Aviontix was a kingdom so long ago, that everything has been looted. (Figure there has been a whole historical epoch 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 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.

Aviontix is designed to be an "ancient kingdon" to be inserted into a game world as history. However, you can make it a current game world, if you want.