John 21:11 with its mention of a catch of 153 fish is considered to be
a reference to the "measure of the fish" which was also a sacred number in Pythagorean geometry. According
to Plato, the selfsame story is told of Pythagoras helping his followers
to fill their nets.
The measure of the fish was a formula known to Archimedes in the third
century BC.
It is derived from two overlapping circles where the overlap is known
as the *vesica piscis*, the bladder of a fish, from its similarity to the
shape of a fish. It is also known as the *mandorla*, Latin for almond.

Inside this intersecting area, in addition to the
triangle, the tetrad, the square, the pentacle, and many more polygons,
the width to height ratio is 265:153 and, geometrically, the ratio of
these dimensions is the square root of 3.

Symbolically, one sphere represented the Supreme Being, the second
circle the goddess and the overlap, with its obvious similarity to
the vulva, the creation of their offspring.

Early Christians used the symbol as a method to describe the coming together
of heaven and earth, between the divine and human, or spirit and matter.
They also used it to make themselves known to each other by scraping two lines
indicating a stylised fish on a wall. One would make a small circle and the next
to pass by would make a another slightly overlapping circle thus completing the
vesica piscis.

See also St Peter