In Greek philosophy, it is generally taken that the line and the circle form a contrary. For example in Aristoteles Physics generally takes that motion can be formed out of this contrary, and this is affirmed in Newtonian Mechanics where the general motion of a body is decomposed into rotational and linear motions.
In the Platonic dialogue, Parmenides, he defines the circle and straight line as:
a. The round is that which all the extreme points are equidistant from the centre.
b. The straight is that in which the centre intercepts the view of the extremes.
In this picture, the straight line appears as a 'degeneration' of the circle; this to me at least appears implicitly, given the language that Parmenides uses; is there definite textual evidence that this is the case?