At Tawheed - Unification Ar-Ruba' Al Khal Empty Quarter Painted by Gerhadt Liebmann Ar-Ruba’ Al Khali is the vast sand sea of southern Saudi Arabia known as al ahqaf of the Arab geographers. The wind-blown dunes rise as high as 300 meters in places and the sands extends from the foothills of southern Hijaz to the highlands of Oman.187 X 141 Photograph by Humberto Da Silveira