There must have been small garrison towns scattered along the length. There were not many farms or trade towns to provide ease, relaxation and food for soldiers and workers. The supply trails were over mountains along narrow paths. To bring supplies to the top, ropes were slung over posts set in the Chinese side of the wall and baskets were hauled up hand over hand. Supplies must have always been short and chancy, particularly in the winter.
History seems to suggest that the wall worked well.
Only when a dynasty had weakened from within, were invaders from the north able to advance and conquer. The fact is, that the cost of the wall's construction bankrupted Dynasty after Dynasty. Invaders, such as the Mongols, took advantage of rebellion from within and stepped into the void of power without extended wars. Over the past few centuries, the Great Wall has served as a source of building materials for local farms and villages. The same brutal isolated conditions which made the Great Wall a triumph of engineering and determined planning make restoration problematic and slow.