The origins of Hinduism can be traced back to the Indus Valley civilization and the arrival of the Aryans in India in around 1500 BCE. The Aryans developed the caste system and their religious beliefs were documented in the Vedas. Key Hindu texts like the Upanishads and Bhagavad Gita explored philosophical concepts like Brahman, karma, dharma and samsara. In the post-classical period, Hinduism evolved to emphasize devotion to major gods like Brahma, Vishnu and Shiva. Modern Hinduism has been influenced by encounters with other religions and grapples with issues like the caste system and role of Hinduism in a democratic India.