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Rivers exist. That statement would be regarded as a solid fact by almost every normal person.

What is a river, exactly?

All rivers on earth are fluid that is flowing, (Not just water; Have you ever seen a river of LAVA?)
impelled by the force (law) of gravity. A river isn't a thing, it is a state of being-the action of a physical entity. The water isn't a river, then it is, then it is gone. The water is temporary. The river is permanent, though following a slowly changing path.

Civilization is people; people obeying certain rules, following a certain, but slowly changing, path. The people are temporary. The Civilization is permanent (by the relative standard of a human lifespan.)

We have only to follow the course laid for us by the great men and women who came before us.

Time does not drive us forward, Civilization does.