Full Idea
An infinite circle is impossible, since any circle is bounded by its circumference.
Gist of Idea
Circles must be bounded, so cannot be infinite
Source
Gottfried Leibniz (Dialogue on human freedom and origin of evil [1695], p.114)
Book Reference
Leibniz,Gottfried: 'Philosophical Essays', ed/tr. Arlew,R /Garber,D [Hackett 1989], p.114
A Reaction
This is interesting if one is asking what the essence of a circle must be. If is tempting to say merely that the radii must be equal, but can they have the length of some vast transfinite number? The circumference must be 2π bigger.