Nowadays, lots of Libya, Tunisia, and Algeria are inhospitable on account of the progressive desertification of North Africa, but in the ancient world, these were quite rich areas; wikipedia [which is always totally reliable, I know] says there are archaeological finds that confirm large scale habitation in now hostile terrain. What was the terrain like in say Libya during the Roman empire? It doesn't seem like it would have any rivers draining the area; was it just a coastal plain? Did they just rely on rainwater for growing crops?