 The idea of Brahman was birthed in the Rig Veda (ca. 1000–1500 BCE), was defined in the Upanishads (ca. 500 BCE), came to full flower in the Bhagavad-Gita (ca. 200 BCE) and the Brahmasutras (400–450 CE), and has been refined in commentaries about them for over the past millennium, first by Adi Shankara (788–820 BCE) and then by many others after him which constitute the Vedanta system of Hindu philosophy (Vedanta = “end of the  Vedas”).[25]  Vedanta has been dominant among the traditional six Hindu philosophical systems for at least the last 500  years.[26]