Originally a Hegemony terraforming failure, the people who inhabited the world (mostly Suni Muslim engineers) persisted and after time of The Fall, they succeeded in transforming the planet from a frozen wasteland with ice-crystal hurricanes and methane-ammonia glaciers, into a Lap tundra world with breathable air, and even adapted Old Earth flora and Fauna (such as the woolly mammoth and horses) occupying the millions of hectares grasslands and equatorial highlands.
The extensive grasslands in the planet's southern continent were home to millions of Old Earth horses bred by the original colonists. The enormous horse herds lived in a type of symbiosis with nomad bands. The high foothills along the world's equator were home to farmers and city folks. 
The world was home to violent predators created by centuries of accelerated ARNying, such as "mutant carrion-breed packs", and "burrowing night terrors", as well 30-meter long grass serpents evolved from Hyperion's Sea of Grass. Other predators included Rock Tigers from Fuji, smart wolves, and IQ-enhanced grizzly bears.
Instead of extinguishing the predators, the population of Groombridge Dyson D chose instead to carefully protect the horse herds while at the same time building a great wall that eventually grew to be over 5,000 km long, separating the predator-filled highlands from the horse-herd savannas and forests. The wall eventually became a great city itself, also called Groombridge Dyson D. The city would eventually grow to be thirty meters tall at its lowest, filled with mosques and decorated with minarets, with wide travelways at its top in which chariots would travel. The work was primarily done by robots and Androids.
Aenea and her friends worked on the construction of that wall for six standard months. Aenea left her friends and A. Bettik there for a period of time while she went on a lonely voyage to a location only revealed at the end of The Rise of Endymion. There, after centuries of searching, A. Bettik found his two crèche siblings on this planet: A. Antibbe, his brother; and his sister, A. Darria.