The Sumerian King List opens with a claim that sets its whole structure: "when kingship descended from heaven," it was first held at one city alone, before passing in unbroken sequence, city to city, king to king, never held by two places at once. That framing device lets the list run through a series of antediluvian rulers, kings said to have reigned before a great flood, each assigned reign lengths in the tens of thousands of years, figures no historian reads as literal chronology. The flood itself appears as an explicit narrative break in the text, after which "kingship again descended from heaven" and a fresh sequence of dynasties begins, at Kish first in most exemplars, with reign lengths that shrink, gradually and unevenly, from the mythic scale of the earlier kings toward something closer to a normal human lifespan.
As the list moves further from the flood, its later entries increasingly overlap with kings independently attested in inscriptions, building dedications and administrative records, so the text does not divide cleanly into a mythical half and a historical half; it shades from one into the other, with the exact boundary a matter of ongoing scholarly judgment rather than a line the text itself draws. Roughly twenty exemplars of the list survive on clay tablets and one cylinder-shaped prism, the Weld-Blundell Prism now held in Oxford, the most complete single copy, and comparing them shows real disagreement in names, order and reign lengths between different scribal traditions rather than one stable, universally copied text.