Why They Built that Giant Wall

d12
1. Shield against much-publicized catastrophic flood event that will not occur for another thousand years
2. To protect the Crypts of the Gods from unwanted intrusion
3. To keep the dinosaurs in: inner wall festooned with special anti-lizard weaponry
4. To keep the land's titanic original monarch out: loaded w/warding magic
5. As a barrier against the highly aggressive, intellectually challenged martial society teeming beyond
6. Remnant of continent-encircling anti-magic dome of the ancients
7. To direct lava flows from currently dormant volcano as aqueduct toward enemy cities
8. Following commandment from deity, to divide the people into divergent tribes for an inscrutable purpose
9. Civilization A was all about loud parties and blood sacrifice, civilization B thought the generations-long wall project well worth the effort
10. Gigantic toll wall erected by giants back in their entirely forgotten heyday
11. As a winding temple to once-preeminent snake god, whose vast skeleton remains housed within
12. To permanently isolate hermetic order of yeti ascetics, largely successful, much serenity beyond