From FreeSpace Wiki
Not much was left of the culture of the Ancients, only fragments of buildings, tombs, and pieces of crashed ship debris. The only way we can learn from the history or the culture of the Ancients is to examine the artifacts they left. Artifacts were found in Altair, Deneb, and Aldebaran, though we are perfectly sure the empire of the Ancients was larger and more powerful than the Galactic Terran-Vasudan Alliance.
What they willed to leave for posterity, they crypted them into their artifacts. We first learned about the ancient civilization when Vasudan refugees found a strange device of unknown race in the Altair system. Decrypting such artifacts was the key to defeat the SD Lucifer and win the Great War.
Additional findings by expedition teams revealed a small amount of information about the Ancients, even though a large number of findings have been classified on high security levels. The GTVA uses Minoan names to designate Ancient artifacts.
It is also known that the Hammer of Light used an Ancient temple as headquarters.