Who said they crossed the Sahara? They originally came by boat, and they can also go through the Serengeti plains
You have to cross the Sahara by going through land. You can also go from East Africa and Djibouti (the best country).
Like I said, the Serengeti Plains in East Africa. Travel south from Somalia, cut west toward Lake Victoria, then cross to the Congo Basin. And I'm pretty sure some Arabs and Turks can cross a desert