98 THE FUTURE OF ARID LANDS 
Archaeological and Historical Studies 
It happens that most of the arid zones were, in the past, seats of 
very advanced agricultural civilizations, remains of which are well 
preserved. This is true in North Africa, in all the countries of the 
Near East, in India, etc. 
The disappearance of these civilizations receives two explana- 
tions: the first attributes it to variations in the climate; the 
second, to human factors. We believe that it has been shown that 
the second is more probable. It is true for North Africa, and the 
reclamation of Tunisian lands was very much facilitated by 
using archaeologicalinformation. The planting of olive trees in the 
Sfax region was decided upon because ruins of oil presses lay 
scattered about the surface. As it has happened, the olive trees 
have prospered in dry farming when they were planted with 
the same spacing as that recommended by the Phoenician and 
Roman agronomists. 
At present, every year, many wells or water projects are carried 
out by using as base the indications given by Roman ruins. 
For example, in regions where no wells are found, but only ruins 
of cisterns, cisterns must be constructed or water must be 
sought at depths greater than those reached by Roman techniques, 
which, however, took advantage of phreatic water levels by 
means of wells more than 100 meters deep. 
Irrigation, both by perennial or flood waters was practiced 
also, with techniques that have survived in certain spots up to 
our epoch and that are always useful of application. It therefore 
pays to begin research for the development of an arid country 
by establishing an archaeological survey directed toward water 
resources. This survey 1s now made easier by using aerial photos 
on which appear the limits of the fields, and traces of plantations 
cultivated even many centuries ago. 
Thus we know that in certain steppe regions the population in 
antiquity was more numerous than it is now and therefore can 
be increased. 
Problems of Salinity 
The complete utilization of water means the recovery and 
reutilization of already used water. This part of the program is 
