[hinkley]

Unfortunately the ancients didn't invent calculus. Pi had been in use a long time when Liebniz and Newton came along.

[deathanatos]

Another way to look at that would have been visible to non-calculus bearing ancients:

  A = πr²
  C = πD

… why do we arbitrarily use r in one equation, and D in the other? (… because we're using the wrong constant, and it bugs us, and we're sweeping that under the mathematical rug.)