composed before 5th-century BCE, the term Dhyana and the related terms such as Dhyai (Sanskrit: ध्यै, deeply meditate) appears in numerous Upanishads composed after the 5th-century BCE, such as: chapter 1 of Shvetashvatara Upanishad, chapters 2 and 3 of Mundaka Upanishad, chapter 3 of Aitareya Upanishad, chapter 11 of Mahanarayana Upanishad, and in various verses of Kaivalya Upanishad, Chulika Upanishad, Atharvasikha Upanishad, Brahma Upanishad, Brahmabindu Upanishad, Amritabindu Upanishad, Tejobindu Upanishad, Paramahamsa Upanishad, Kshuriki Upanishad, Dhyana-bindu Upanishad, Atharvasiras Upanishad, Maha Upanishad, Pranagnihotra Upanishad, Yogasikha Upanishad, Yogatattva Upanishad, Kathasruti Upanishad, Hamsa Upanishad, Atmaprabodha Upanishad and Visudeva Upanishad. Brahma Sutras The Brahma-sutras, which distills the teachings of the Upanishads and is one of three foundational texts of the Vedanta school of Hinduism, states that Dhyana is not Prativedam (or, one for each Veda), and meditation belongs to all Vedic schools. Adi Shankara dedicates an extensive chapter on meditation, in his commentary on the Brahma-sutras, in Sadhana as essential to spiritual practice. His discussion there is similar to his extensive commentary on Dhyana in his Bhasya on Bhagavad Gita and the early Upanishads. Dharma Sutras The verse 30.8 of the ancient Vasistha Dharma-sutra declares meditation as a virtue, and interiorized substitute equivalent of a fire sacrifice. Bhagavad Gita The term Dhyana, and related words with the meaning of meditation appears in many chapters of the Bhagavad Gita, such as in chapters 2, 12, 13 and 18. The chapter 6 of the Gita is titled as the "Yoga of Meditation". The Bhagavad Gita, one of the three key books of Vedanta school of Hinduism, states four Marga (paths) to purify one's mind and to reach the summit of spirituality – the path of Unselfish Work, the path of Knowledge, the path of Devotion and the path of Meditation (Dhyana). Huston Smith summarizes the need and value of meditation in Gita, as follows (abridged): Meditation in the Bhagavad Gita is a means to one's spiritual journey, requiring three moral values – Satya (truthfulness), Ahimsa (non-violence) and Aparigraha (non-covetousness). Dhyana in this ancient Hindu text, states Huston Smith, can be about whatever the person wants or finds spiritual, ranging from "the manifestation of divinity in a religious symbol in a human form", or an inspiration in nature such as "a snow-covered mountain, a serene lake in moonlight, or a colorful horizon at sunrise or sunset", or melodic sounds or syllables such as those that "are intoned as