|Location:|| Milky Way Galaxy|
|Species:||100% human variants|
|Defenses:||Castalian Republic corvettes|
Castalia is the homeworld of the water-breathing Castalians.
Water coverage: 93%
Castalia was a major population center during the Commonwealth era. Castalia's vast oceans were settled by humans genetically engineered to breath water, with air breathers (the minority) living on the islands and space-designed human variants living in numerous orbital habitats. After the Commonwealth's fall, Castalia was enslaved by Nietzscheans of the Volsung Pride. The brutal occupation lasted over 200 years and ended with a successful revolt that culminated in the destruction of the Volsung Aerie Orbital Platform and the death of its 75,000 inhabitants, almost a third of them slaves. More recently, the Castalian Republic became the second government to sign the charter for a restored Systems Commonwealth.
- Castalia was a water nymph.