In the 1930's an American agronomist and proto-environmentalist bythe name of Walter Lowdermilk visited Mandatory Palestine as part of a world-wide survey he was doing for the American Department of Agriculture. He was deeply impressed by the efforts of the Zionist pioneers to roll back the desert and rejuvenate agricultural practices. In a subsequent book he postulated that were the land to be treated correctly it might possibly be able to support 8-10 million inhabitants someday.
There are about 12 million today, and growing.
Many years earlier - almost 1,600, to be precise - a movement had begun in which Christian monks and hermits began to settle in the desert to the east of Jerusalem. They were following in the footsteps of earlier monks in Egypt and elsewhere; the ones in the Judean desert wished to live far from the cities and bustle of civilization, but also close enough as to be able to interact with pilgrims and other potential benefactors. At the peak of the phenomenon there were more than a hundred monasteries of varying sizes in the Judean desert. Most of them were destroyed by the Persians in 614, and then were not rebuilt because of the Muslim invasion of 634. Some of them were rebuilt during the Crusader kingdoms of the 12-13th centuries, but then fell into disuse. Today there are six such monasteries, most of them with a single monk or a handful of them at most.
Of course, having 12 million people in a land that used to host a million or two at the best of times, along with the technology to pipe water out into the desert, means the settled areas are a bit larger than they once were.
How much larger? Well, take the large and famous monastery of Euthymius the Great (died in 473).
When Euthymus looked around he saw only desert - which still works if you look north south or east. But not West:
Can one imagine what these monasteries looked like in real life, before they were destroyed? Well, yes. Because to the east of Jericho there's one that's still there (or perhaps, is there again): the monastery of Gerasimus (died 475):
The Desert a City: An Introduction to the Study of Egyptian and Palestian Monasticism Under the Christian Empire, by Derwas Chitty.