Circulation is important because any size or shape of pond will develop slow spots where the water just hangs out, gradually losing oxygen and growing anaerobic bacteria to feed on nutrients in the water. Mosquitoes and other noxious insects are also attracted to still water. Aeration is important as well, because all pond life (except the anaerobic bacteria) require oxygen to survive. Wildlife ponds in nature don’t have mechanical pumps to help them out, but they typically have some sort of natural mechanism that keeps the water flowing - a spring or a river, for example. Ponds without this benefit don’t usually support fish, though. The biological load of fish, with all the waste that entails, will eventually create an environment that is toxic to both fish and plants.
If your ultimate goal is just to reject any modern conveniences, you might find some ancient contraptions that really appeal to you. A fairly simple example is the Heron pump, which originated in Hellenistic Alexandria in the first decades AD. This is not a perpetual motion device, so it will need some help from time to time to keep working, but it operates on gravity and water pressure alone. If you do want to build a pond and eschew use of any kind of artificial support, then a moderately sized wildlife pond without fish is probably the best way to go. For the healthiest environment, it should be heavily planted with a variety of submerged and above water species, with some plants even creating a carpeted effect to cover about ⅔ of the water surface. This prevents sunlight from reaching algae. You’ll need plenty of rocks and other surfaces to support beneficial bacteria as well. While this kind of pond can’t support fish, other wildlife can be perfectly happy there - turtles, dragonflies, frogs and salamanders, to name a few.
