321 BC
The Mauryan empire founded by Chandragupta Maurya which was controlling the Central, western and the eastern India that days. This empire got top of the success under the Emperor Ashoka the Great, who seized power in 272 BC. He afterwards extended his empire from Mysore to the Himalayas and form Assam to Afghanistan. In 260 BC after the destructions by unrelenting conquests in the battle of Kalinga, Ashoka converted to Buddhism.
Then he restructured his rule and started encouraging the crafts, arts as well as the architecture. Ashoka then actually started new political and social systems and visit through missionaries to Sri Lanka and Nepal in order to propagate the Buddhism.
The Greek representative Megasthenes was so impressed that he had done various recordings related to descriptions of the wealth in the capital Patliputra now known as Patna. There are many things like pillars, stupas and edicts scattered in the whole country in Sanchi, Sarnath and Mathura adds a glimpse of the enormousness of the Mauryan Empire.
Four lions sitting back to back on the top of abacus decorated with a band of designs and sentence 'Let truth alone triumph' inscripted is the seal of modern day India which is also the Emperor Ashoka's standard.