Just as a woodworm bores through the wood creating some sort of a shape, the Pranavayu (the life force), when it travels through the Chakras creates a distinct pattern. And this shape or pattern of its movement resembles the shape of particular letters of the ‘Devanagari’. Hence the pathway of that Chakra has been assigned that particular letter of the Devanagari script. The Mooladhara Chakra consists of four Padmadals or petals. When Pranavayu travels through the Mooladhara Chakra, the shape of the letters “वँ, शँ, सँ, षँ” of Devanagari is formed in the four petals of this Chakra. The Swadhisthana Chakra has six petals, when Pranavayu travels through this six petals, it forms the shape of the letters “बँ, भँ, मँ, यँ, रँ, लँ”. The Manipur Chakra consists of ten Padmadals or petals whose letters are “डँ, ढँ, णँ, तँ, थँ, दँ, धँ, नँ, पँ, फँ”. The Anahata Chakra has twelve Padmadals or petals. When Pranavayu travels through this Chakra the twelve letters thus formed are “कँ, खँ, गँ, घँ, ड़ँ, चँ, छँ, जँ, झँ, ञँ, टँ, ठँ”. The Vishuddhi Chakra consists of sixteen Padmadals, and when Pranavayu travels through this Chakra, the shapes of sixteen letters from the Devanagari alphabet from “अ” to “अः” are formed. Agya Chakra has two Padmadals or petals and its letters are “हँ” and “क्षँ”. The Sahastrar Chakra is composed of thousand-petals and all the letters of the Devanagari alphabet are repeated when the Pranavayu or the life force moves through its thousand petals. Apart from these letters, shapes of different angles are also formed in the chakras due to the flow of the Pranvayu or the life force. Just as in a fast flowing river, whirlpools occur and the design that gets formed in the vortices are sometimes shallow, diagonal, round, or square, similarly, when the Pranavayu passes through these Chakras, it creates a kind of subtle whirlpools whose shapes are like different types of triangles, quadrangles and hexagon etc. These figures are called the Yantras of the Chakras. Due to the flow of the life force, the shape of a quadrangle is formed in the Muladhara Chakra, hence the Yantra of the Muladhara is called Chatushkona or quadrangle. Similarly the Yantra of the Swadhisthana Chakra is a crescent. The Yantra of the Manipur Chakra is a triangle. The Yantra of the Anahata Chakra is a hexagon, the Yantra of Vishuddhi Chakra is spherical. The Yantra of the Agya Chakra is oblong and the Yantra of the Sahastrar Chakra resembles the full moon.
~ Acharyasri