Men have looked upon the desert as barren land, the free holding of whoever chose but in fact each hill and valley in it had a man who was its acknowledged owner and would quickly assert the right of his family or clan to it, against aggression.

Lawrence is correcting an outsider’s colonial assumption that deserts are “empty” and therefore available for occupation. He argues that what appears unowned to a distant observer is, on the ground, densely mapped by customary rights: hills, valleys, wells, and grazing routes are embedded in kinship, honor, and clan jurisdiction. The point is both anthropological and political. It explains why attempts to treat the desert as a blank space—whether by travelers, administrators, or armies—provoke swift resistance, because they collide with an existing, locally recognized system of property and sovereignty. The quote thus reframes “barrenness” as a visual illusion masking social and territorial order.