Lore - Capaloptocus/wordsofradiancemod GitHub Wiki
According to lore, mankind finally won the war against the voidbringers, and the Heralds went to the Tranquiline Halls to try to drive the voidbringers out from there too. This is a lie.
Whenever a Herald dies, their soul would be sent to Braize, the planet more commonly called Damnation in Vorin mythology. On Braize, the Heralds would be tortured by the souls of the Fused, those called voidbringers by mankind. At the end of each Desolation, any Heralds who hadn't been killed would voluntarily return to Braize to be tormented. The souls of the ten Heralds acted as a lock, preventing the Fused from leaving Braize. In that place, the ten of them held back the darkness. This lasted until one of them, unable to withstand the torture any longer, gave in. Then the Fused would return to Roshar to wage war on humankind, and the Heralds would return to train and help the Knights Radiant to fight the Fused. Then the Heralds would die or return, and trap the Fused on Braize for as long as they could endure. And so on, and so on.
This continued until what would become known as the Final Desolation, Aharietiam. By the point, centuries of torture had worn against the Heralds, and they were shadows of what they used to be. The last few times, there would be barely a year between desolations before one Herald or another broke, and sent them all back. On the day of Aharietiam, the Heralds met after the battle and found that, remarkably, only one Herlad had died. Taln, Herald of the Common Man, had a habit of choosing impossible positions to defend, and winning. He also had a habit of dying in the process.
The nine remaining Heralds also realised that, in all the time that they had existed as they were, there was only one Herald who had never broken. Only one who had never given in to the torture of Braize and allowed the Fused to return. And so, they made a terrible decision. Each Herald broke their bond with their Honourblade, and drove it into the stone of the place where they were gathered. They then left them there, a circle of nine swords in the stone, with an empty place for the tenth. Then, they all turned in a different direction, and walked away. Leaving Taln to hold back the army of voidbringers alone. Which he did - for four and a half thousand years.