It has often been suggested that the great prosperity of this region under the Empire was due to a climate superior to that of to-day; that there was in fact a more abundant rainfall and a more equable temperature. The Romans left us no weather statistics (an essentially modern passion), and such evidence as we have appears to be against the theory. The lakes in the province of Constantine were no greater than they are to-day; Roman ruins on their banks attest this. Roman bridges exist here and there throughout the country, and they were not designed to span wider rivers or to resist heavier floods. But this does not settle the matter. It is certain that there was far more timber; the Arab has continually destroyed and he does not plant. The rainfall of to-day is probably less continuous and more uncertain. Yet we cannot believe that the climate is seriously changed. Sallust complains that in Africa both sky and earth have too little water. But the Romans made the best of what there was. The remains of their canals and cisterns are everywhere. In the country to the south of Sétif they dug hundreds of wells, many of which still exist. They barred the course of rivers and created reservoirs. Their extensive works of irrigation are described by Procopius, and appear to be exactly similar to those now in use. Elaborate water-rights existed. A monument found at Lambasba sets forth the number of olives and fruit trees which every farmer possessed and the number of hours of running water to which he was entitled. This system of reckoning a right to water-supply by hours is still in vogue in the island of Madeira, and probably elsewhere. Every effort was made to encourage planting. Exemptions from taxation for a certain number of years were granted to cultivators who planted vines or olives, or grafted the wild olive. Olive oil was exported to Rome in enormous quantities; fragments of jars found in the Tiber bear the mark of Tubusuctu, a town near Bougie. Such facts go to show that the great prosperity of North Africa was rather due to intelligent use of its resources than to any superiority of those resources. This prosperity seems to have reached its culminating point under the dynasty of Septimius Severus, himself a native of Africa. The fact that he died at York illustrates the extent of his empire. He and his son Caracalla showered favours on their compatriots, as numerous inscriptions attest.