It is not exactly clear when the Bhagavad Gita was written. Astronomical evidence cited in the Mahabharata place the incidents upon which the Gita is based around the time 3100-3150 BC, while the Puranas suggest a date of c. 1924 BC. Scholars place the actual writing of the Gita in the latter half of the 1st millennium BC (roughly 4th century BC), making it a contemporary of the older Upanishads.