Chiliagon

A whole chiliagon is not visually discernible from a circle. The lower section is a portion of a chiliagon, 200 times larger than the smaller one, with the vertices highlighted.

In geometry, a chiliagon (pronounced /ˈkɪli.əˌgɑn/) is a polygon with 1000 sides. The measure of each angle in a regular chiliagon is 179.64°.

René Descartes uses the chiliagon as an example in his Sixth meditation to demonstrate the difference between pure intellection and imagination. He says that, when one thinks of a chiliagon, he "does not imagine the thousand sides or see them as if they were present" before him -- as he does when one imagines a triangle, for example. The imagination constructs a "confused representation," which is no different from that which it constructs of a myriagon. However, he does clearly understand what a chiliagon is, just as he understands what a triangle is, and he is able to distinguish it from a myriagon. Therefore, the intellect is not dependent on imagination, Descartes claims, and it is able to entertain clear and distinct ideas when imagination is unable to.