The bahro are a race of intelligent, bipedal creatures who were somehow enslaved by the D'ni through the use of a stone Tablet. According to a D'ni survivor named Esher, they originally came from the Age of Noloben. Their name comes from the D'ni "bah" (ba), meaning "beast".
Bahro are vulnerable to the venom of a particular black-and-yellow-striped snake that lives on Noloben. This venom can completely paralyze them and nullify their linking abilities, and they are frightened even by the depiction of the creature.
Although they are very secretive towards humans, bahro are quite social towards each other, and call to each other via racoon-like screeches, growls, purrs, and chirps. The existence of a number system indicates that they can count, they use art—not unlike primitive human cave paintings—to record stories, and they use ideograms and pictograms are a form of written communication. Yeesha is also able to communicate with them verbally, so they are clearly capable of understanding other languages as well.
Bahro possess the unique ability to link at will, both between Ages and from place to place within the same Age, without the need for Linking Books. This ability seems at least in part to be a property of their skin, as a strip of bahro hide on his cloak enables Esher to link in a similar fashion. They can also manipulate the Ages themselves, triggering rainstorms, starting windstorms, revitalizing a geothermal heat source, or even altering the flow of time.
For 10,000 years, the bahro were enslaved under the power of the Tablet. No one is quite sure what the Tablet is, but some have speculated that it is a sacred relic of the bahro. Whether or not the Tablet literally binds the bahro, or whether they simply worship it, it is quite clear that whoever controls the Tablet can rule over the bahro. It is unclear exactly why the D'ni chose to enslave these beings, though it may have something to do with their linking abilities.
The enslavement of the bahro was a secret so tightly kept that their existence was unknown even to most of the D'ni populace. Even the DRC have only unearthed passing references to "the least" in D'ni's historical records.
The bahro were utterly forgotten after the fall of D'ni. Over 200 years later, Yeesha found them and the Tablet while pushing the boundaries of regestoy with a surviving D'ni writer, Calam. After Calam's death, Yeesha learned from them, coming to understand their long suffering and even acquiring some of their abilities herself.
When human explorers began to trickle into D'ni in 2003 CE, she created a journey for them to undertake. The purpose of the journey was to help her bring the bahro one by one back into the D'ni cavern through the use of four special pillars. The exact relationship between the bahro and these pillars is not understood, but Yeesha makes statements which seem to imply that the "soul" of a bahro is somehow tied to them.
In her attempt to free the bahro from their enslavement to the Tablet sometime in 2003–2004 CE, she was seduced by its power and ultimately failed. In 2005 CE, she sought the help of Dr. Richard A. Watson, former leader of the DRC, to help her. Dr. Watson was successful, and the bahro were finally freed when he returned the Tablet to them willingly, rather than keep it for himself.
No longer subject to the Tablet's control, the bahro were divided over how to cope with their long abuse at the hands of the D'ni. Most wished to move on, leaving their past in the past. Another faction, which Yeesha called the bahro nekisahl, desired vengeance against their former masters. These conflicting views eventually escalated into a full-scale civil war between the two factions which spanned the Ages and even made its way to Releeshahn.
For several months in 2007 CE, the civil war intruded into the D'ni cavern. It was only after Yeesha used herself as bait that the bahro nekisahl departed. Since then, there has been no word from her, and there have been no sightings of the bahro in the cavern. The current state of their civil war is unknown.