Terahnee was the Age to which the majority of the Ronay fled when it became clear that their home, Garternay, would soon no longer be habitable. In the shared Terahnee and D'ni language, its name means "the new tree".
Terahnee was a land of rolling fields and open plains. Brilliant white-stone estates dotted the landscape, and were connected with a network of canals. The capital city was described as a "magnificent pile" of stone buildings that dwarfed all of D'ni. It was a land of plenty and leisure for the Terahnee, who numbered over 200 million.
Hidden from view, however, was the slave labor which underpinned the entire Terahnee society. Tunnels for the relyimah ("the unseen") to carry out their labors were hidden within the walls of every building, beneath every field, and beside every canal.
Terahnee society was strictly divided into classes based mainly on a person's Age of origin. The Terahnee controlled the land, and were the only ones considered to be citizens. Like the early D'ni, they were ruled by a king. Their servants, the P'aarli, were from another Age called He'darra. Servants were treated fairly well, and were responsible for overseeing the bulk of the manual labor that the Terahnee deigned beneath their status to complete. The P'aarli were also responsible for the brutal subjugation of the massive population of slaves who kept Terahnee's gleaming edifice running. These slaves, also called ahrotantee—"outsiders"—were poached from countless other Ages and forced to live in squalid conditions well out of sight of their masters.
Terahnee was founded and first ruled over by "the Nameless King" nearly 10,000 years ago. It is likely that this first king of Terahnee was also the last king of Garternay, but their names have both been lost to history. For hundreds of years, the new Terahnee people kept an open link with their cousins, the D'ni, who fled from the same calamity to Earth. This link was permanently severed when the D'ni king Ahlsendar had the Temple of the Great King sealed in 1501 DE with both himself and the Terahnee Book inside. Ahlsendar had previously said that D'ni should seal away its connections to its past.
Rediscovery and downfall
When Atrus attempted to rebuild D'ni in the 9460s DE, he and his companions uncovered the Tomb of the Great King while excavating debris around the D'ni Guild Hall. Inside, they found the Terahnee Book, and sent a small expedition to the Age to explore it. They also unwittingly brought with them a stomach bacterium that was almost universally lethal to the Terahnee people. Over 99% of the Terahnee perished in the weeks following Atrus' arrival, and the relyimah rose up against the now-diminished P'aarli and their absent masters. Event after the deaths from the plague and the uprisings were accounted for, over two billion former slaves were left alive.
A year after Atrus and his party first set foot in Terahnee, they left it again, this time in the hands of its former slaves. In that time, they took upon themselves the re-shaping of the land for their own needs, using their former masters' palatial houses as local government headquarters. Their leaders renamed the Age Devokan, the D'ni word for "hope". The link back to D'ni was re-sealed after the D'ni departed, and no further information about the Age or its inhabitants is available.