The earliest civilization of India were the Harappans. Pakistan was once part of India so the Harappans were also in what is now Pakistan. They were advanced and traded with Mesopotamians, they had a city called Mohenjo Daro. They had jewelery like Lapis Lazuli and also had bathhouses. This city was eventually destroyed by the Aryans, invaders from Central Asia. The Aryans took over India in 1600 AD and went into the iron age in 1100 BC.
Most of Western India was conquered and taken over by the Persians in 513 BC. By 511 BC (the current year in RP), much of India was converted to Buddhism. Before Buddhism came, India was primarily Hindu, as Islam did not arrive until medieval times. In this time period, Sanskrit and Vedic Sanskrit were the spoken languages.