Also known as Sri Chakra, is called the mother of all yantras because all other yantras derive from it. In its three-dimensional forms, Sri Yantra is said to represent Mount Meru, the cosmic mountain at the center of the universe.
The Sri Yantra is conceived as a place of spiritual pilgrimage. It is a representation of the cosmos at the macrocosmic level and of the human body at the microcosmic level (each of the circuits corresponds to a chakra of the body).
Chandra the Legend:
Lord Ganesha was riding home on his mouse after a big feast. A snake slithered into their path. The mouse tripped and Ganesha fell. And guess what .. Ganesha had eaten so much, that his tummy split open and all the Kudumulu tumbled out!
Chandra (the moon god) was watching from the sky. He found this quite funny and started laughing. This made Ganesha mad. He said, “You find it funny that I fell down? Well, I shall banish you from the sky. Then you will not laugh at anyone again!”
Suddenly the night was dark. There was no longer a moon in the sky. This went on night after night. Chandra, and all the Devas (gods) went humbly to Ganesha. They begged him to let the moon back into the sky.
Ganesha relented. He allowed the moon back into the sky. But to remind him to be humble, Ganesha put a curse on him. He would never again shine, full and round every day. Instead, he would become smaller until he disappeared; and then grow again to his full size.