He reigned for HOW long?

The SKL [Sumerian King List] is comprised of two different types of material: lists containing the names and provenance of kings and length of their rule, and also epic and legendary material dealing with some of the kings. The amalgamated new “genre” is one of a list of kings and their rule, interspersed with brief legendary comments throughout. Each of the kings in the list has an unusually long reign attributed to him, by far the longest reigns coming in the antediluvian period (most numbering in the tens of thousands of years). After the flood, the lengths of reign diminish significantly but still remain unrealistically large for a while (most reigns are in the hundreds, still others are in the thousands), though as the list nears the present the reigns become progressively more believable. — Toward a Poetics of Genesis 1-11, page 182

<idle musing>
Sounds a lot like the genealogies in Genesis, doesn't it...

Numbers are used symbolically in the Hebrew Bible; they weren't mathematicians and they weren't obsessed with dates the way we are. We need to stop reading our presuppositions back into the text!
</idle musing>