text: Upanishad Period According to Williams, from 900 to 600 BCE, the protests of the populace against sacrifices made towards the Vedic gods and rebellions against the Brahmin class led to the embrace of reform by the latter and the composition of the fourth Veda and the Vedanta texts. About half of the Upanishads were mystical and unitive, speaking of experiencing the divine as the one (ekam), while the other half promoted devotion to one or more deities. New gods and goddesses were celebrated, and devotional practices began to be introduced.
  Sramanic movements
  Elements such as those emerging from Buddhism and Jainism made their "heteroprax" contributions to later Hindu mythology, such as temples, indoor shrines, and rituals modeled after service to a divine king. Renunciate traditions contributed elements that questioned sacrifices and the killing of animals, and promoted asceticism and vegetarianism. All of these themes would be incorporated by the Brahmin classes into the later Hindu synthesis, which developed in response to the sramanic movements between ca. 500–300 BCE and 500 CE, and also found their way into Hindu mythology.
  Epic Period
  The era from 400 BCE to 400 CE was the period of the compilation of India’s great epics, the Mahabharata and Ramayana. These were central manifestations of the newly developing Hindu synthesis, contributing to a  specific Hindu mythology, emphasising divine action on earth in Vishnu's incarnations and other divine manifestations. The lore of the devas and the asuras expanded. Epic mythology foreshadowed the rich polytheism of the next two periods. The Mahabharata contained two appendices that were extremely important sources for later mythological development, the Bhagavad Gîta and the Harivamsa.