A stage known as the Vedic period began as early as 4000 B.C.E. (Some Indian scholars push the origins back as much as three or four thousand years before that.) Archaeological evidence from Harappa and Mohenjo Daro point to a highly developed civilization in the Indus river valley from around 2700 to 1500 B.C.E. Early texts suggest a religious culture centered on worship of numerous deities associated with forces of nature. Around 2000 B.C.E., there may have been a major population shift from the northwest of India to the Ganges plain as a result of the drying up of the Sarasvati river, once a prominent feature of the Indus valley. The Vedic period comes to a close around the time of that shift. The period of the Upanishadic scriptures and the Epic age, from 1500 to 500 B.C.E., witnessed dramatic changes and the evolution of major new forms of religious expression. During these centuries, the Upanishads developed the speculative approach now known generically as Vedanta, the “culmination of the Vedas.” For the next millennium or so (500 B.C.E.-500 C.E.), sometimes referred to as the Classical Period), new post-Vedantic sacred texts, called Sutras, Shastras, Agamas, and the earliest Puranas, formed the bases of a number of important schools of thought. From this period, too, came the written Epics, the Ramayana and Mahabharata. Between around 500 and 1800 C.E., the so-called Medieval Period, popular devotional theism—based largely on mythic narrative texts called the Puranas—spread across most of India. Beginning with the arrival of the British in the mid-eighteenth century, the Modern Period extends into the mid-twentieth century, the declaration of India’s Independence, and the partition that created East and West Pakistan as separate Muslim states.