From Halopedia, the Halo wiki
Feldokra was colonised by the great sea clans of the Sangheili's past, led by stalwart kaidons who built their homes atop the waters. Those who dwell on Feldokra are strong, rugged Sangheili, who prefer adventure and the beauty of the open seas to the mundanity of terrestial life. The Covenant eventually developed enermous structures across the world's surface, military citadels that would serve the highest echelon of military personnel, second only to the towers of High Charity itself. During construction, the investigations of the San'Shyuum revealed what the Sangheili had not; countless Forerunner fuel stores and power complexes lay deep below in the dark ocean trenches.