The Vesica Piscis is a symbol made from two circles of the same radius, intersecting in such a way that the center of each circle lies on the circumference of the other.

The name literally means the bladder of the fish in Latin. In the Christian tradition, it is a reference to Christ, as in ichthys-- two intersecting arcs that form the almond shape at the center of the Vesica Piscis resembling the profile of a fish, used by early Christians as a secret symbol and is now known colloquially as the Jesus fish.

The Vesica Piscis has been the subject of mystical speculation at several periods of history, perhaps first among the Pythagoreans, who considered it a holy figure. The mathematical ratio of its width (measured to the endpoints of the "body", not including the "tail") to its height was reportedly believed by them to be 265:153. This ratio, equal to 1.73203, was thought of as a holy number, called the measure of the fish.

The geometric ratio of these dimensions is actually the square root of 3, or 1.73205... (since if you draw straight lines connecting the centers of the two circles with each other, and with the two points where the circles intersect, then you get two equilateral triangles joined along an edge). The ratio 265:153 is an approximation to the square root of 3, with the property that no better approximation can be obtained with smaller whole numbers.

The number 153 appears in the Gospel of John (21:11) as the exact number of fish Jesus caused to be caught in a miraculous catch of fish, which is thought by some to be a coded reference to Pythagorean beliefs.