The article is devoted to a complex historical and mythological study of the largest and most ancient epic of Bashkir folklore - the epic "Ural Batyr". The author has revealed some ancient myths underlying the Bashkir epic. The primary myth of a couple of aquatic birds procreating Land and Universe had been coupled with the myth of two demiurgh brothers. The second myth is about the great dual Universal divide, each sphere thereof mastered by Ural and Shulghan. They espouse birdlike maidens symbolizing celestial bodies. Brothers part finally by virtue of the magical wand employed by the elder to strike a crevice in Earth leading to the Nether world. The subterranean waters start a world deluge and mythical dragons crawl out on the Earth's surface. This line of the plot parallels the Ural-Altaic peoples' myths.