Permanent populations are not a sign of civilization. Many religious sites today are sparsely populated except for once/twice a year, but we still have civilization. The Mongols were civilized even when they were raiding the entire old-world and establishing many dynasties. They had writing, religion, generals and well-organized armies, a bureaucracy, laws and customs, tariffs, etc, just not a single plot of land they went to sleep on every single night. Heck, even NYC doubles in population daily [0], those people may be daily commuter nomads, but they are 'civilized' people.

[0]https://cityroom.blogs.nytimes.com/2013/06/03/commuters-near...