India was the one of the largest economies in the world, for about two and a half millennia starting around the end of 1st millennium BC and ending around the beginning of British rule in India. Around 500 BC, the Mahajanapadas minted punch-marked silver coins. The period was marked by intensive trade activity and urban development. By 300 BC, the Maurya Empire had united most of the Indian subcontinent including Tamilakam, which was ruled by Three Crowned Kings. The resulting political unity and military security allowed for a common economic system and enhanced trade and commerce, with increased agricultural productivity.