The Ashoka Chakra is a depiction of the Buddhist Dharmachakra, represented with 24 spokes. It is so called because it appears on a number of edicts of Ashoka, most prominent among which is the Lion Capital of Sarnath.
The most visible use of the Ashoka Chakra today is at the centre of the National flag of the Republic of India (adopted on 22 July 1947), where it is rendered in a Navy-blue colour on a White background, by replacing the symbol of Charkha (Spinning wheel) of the pre-independence versions of the flag.
According to Hindu religion, Puranas mentioned that only 24 Rishis wielded the whole power of the Gayatri Mantra. These 24 rishis in Himalayas are represented through the 24 letters of the Gayatri Mantra. All the 24 spokes of Dharmachakra are the representation of all these 24 rishis of Himalayas, in which Vishvamitra is first and Yajnavalkya is last who governs the religion (Dharma). Ashoka Chakra is a symbol of Dharmchakra and is also known as Samay Chakra in which all the 24 spokes represents 24 hours of the day and symbolizes the movement of the time.
When Buddha achieved nirvana (Enlightenment) at Gaya, he came to Sarnath on the outskirts of Varanasi. There He found his five disciples (panch vargiya Bhikshu) Ashwajeet, Mahanaam, Kaundinya, Bhadrak and Kashyap, who had earlier abandoned him. He preached his first sermon to them, thereby promulgating the Dharmachakra. This is the motif taken up by Ashoka and portrayed on top of his pillars. This is the origin of the chakra in the Indian flag and it asserts the strong ties of India with the Buddhist faith. It is also known as Bhavachakra.
However, the 12 out of 24 spokes represent the twelve causal links taught by the Buddha. The twelve causal links, paired with their corresponding symbols, are: