Here is the full list of all 12 Secrets of the Past: Dion achievements.
Unearth an Artifact
Unearth a fragment of a Philosopher statue
Unearth a complete Mosaic
Assemble a broken statue
Place an Artifact on a Pedestal
Place a Mosaic on the Exhibition floor
Process an Artifact through the Labs
Win the game in EASY mode
Win the game in NORMAL mode
Win the game in HARD mode
Excavate the complete site
Deploy multiple Excavation Grids