This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
Black Tortoise of the North gathers the eighth through fourteenth lunar mansions, the segment of the twenty eight lodge system read as the northern quarter's guardian, a tortoise entwined with a serpent.
Dou, the Southern Dipper, opens the palace in Sagittarius, distinct from the Big Dipper of Ursa Major and associated with measurement and official rank; it is one of the widest lodges in the whole set, since widths vary from over thirty du to barely one depending on how the reference stars happen to fall. Xu, Emptiness, lies across Aquarius and Equuleus in a region with no bright stars at all, and its name records exactly that; associated with death and mourning, it shows the lodges were fixed by what could actually be observed rather than by a scheme requiring every division to be equally furnished. Bi, the Wall, closes the palace with stars in Pegasus and Andromeda, linked to libraries and the storing of knowledge, an association that plays on the lodge's name rather than resting on observation, a kind of wordplay that recurs throughout the almanac meanings attached to the whole system.
Across the seven, faint reference stars in an otherwise empty stretch of northern sky produced some of the widest lodges in the entire twenty eight, and a faint field, however unpromising for naming, made the moon's position against it easier to judge for calendar work.