Great Zab
The boundaries of Uqbar were described using equally nonexistent reference points; for instance, "the lowlands of Tsai Khaldun and the Axa Delta marked the southern frontier". This would suggest that the rivers of Borges' Uqbar should rise in highlands to the north; in fact, the mountainous highlands of eastern Turkey are where not one but two Zab Rivers rise, the Great Zab and the Lesser Zab. They run a couple of hundred miles south into the Tigris.