Abridged History of the 10th Age
The Bâlmyr caverns are located beneath the shores of the Sunholme Sea. They are so called after the city of Bâlmyral, the largest of deep dwarf cities. Bâlmyr was settled in the late Third Age or early Fourth Age during the great expansionary period of the Underland explorers. The underland princes had already been sundered from the surface by that time due to a series of world-rocking earthquakes sometime in the middle Third Age. The proto-empire of the new Stonefathers, first spoken of at Black Delve in the year IV 59 according to the dwarven records I’ve been able to find, was just beginning to form.
Bâlmyr was originally a tertiary arm of the Deep Empire during its heyday, while the central realms around Black Delve were more heavily settled. Bâlmyral served as a stopover city for those caravans en route to the western coast, particularly through the few great cove-caverns that can be found along the shore.
However, the Deep Empire was not fated to last forever. In the late Fourth Age the Night Trolls rose up from the Houses of Night that lay hidden beneath their roadways. I speculate that this occurred at roughly the same time that Tallëor Twice-born destroyed the last of the great Trollish kingdoms on the surface world. This attack was unlooked for, and followed by a series of raids from the Flayers, a race of creatures that had before then retreated before the Deep Empire’s advances.
As though that were not enough, Black Delve was overrun in the first years of the Fifth Age by lost dwarves, their eyes burning and their jaws set in grim silence. From that hour onwards, Bâlmyral, once at the periphery of the Empire, became the largest remaining center of deep dwarf population.