Vedas, the only texts preserved from the early Vedic period and codified between c. 1200 and 900 BCE, contain references to yogic practices primarily related to ascetics outside, or on the fringes of Brahmanism. The Rigveda Nasadiya Sukta suggests an early Brahmanic contemplative tradition. Techniques for controlling breath and vital energies are mentioned in the Atharvaveda and in the Brahmanas (the second layer of the Vedas, composed c. 1000–800 BCE). According to Flood, "The Samhitas [the mantras of the Vedas] contain some references ... to ascetics, namely the Munis or Keśins and the Vratyas." Werner wrote in 1977 that the Rigveda does not describe yoga, and there is little evidence of practices. The earliest description of "an outsider who does not belong to the Brahminic establishment" is found in the Keśin hymn 10.136, the Rigveda youngest book, which was codified around 1000 BCE. Werner wrote that there were According to Whicher (1998), scholarship frequently fails to see the connection between the contemplative practices of the rishis and later yoga practices: "The proto-Yoga of the Vedic rishis is an early form of sacrificial mysticism and contains many elements characteristic of later Yoga that include: concentration, meditative observation, ascetic forms of practice (tapas), breath control practiced in conjunction with the recitation of sacred hymns during the ritual, the notion of self-sacrifice, impeccably accurate recitation of sacred words (prefiguring mantra-yoga), mystical experience, and the engagement with a reality far greater than our psychological identity or the ego." Jacobsen wrote in 2018, "Bodily postures are closely related to the tradition of (tapas), ascetic practices in the Vedic tradition"; ascetic practices used by Vedic priests "in their preparations for the performance of the sacrifice" may be precursors of yoga. "The ecstatic practice of enigmatic longhaired muni in Rgveda 10.136 and the ascetic performance of the vratya-s in the Atharvaveda outside of or on the fringe of the Brahmanical ritual order, have probably contributed more to the ascetic practices of yoga." According to Bryant, practices recognizable as classical yoga first appear in the Upanishads (composed during the late Vedic period). Alexander Wynne agrees that formless, elemental meditation might have originated in the Upanishadic tradition. An early reference to meditation is made in the Brihadaranyaka Upanishad (c. 900 BCE), one of the Principal Upanishads. The Chandogya Upanishad (c. 800–700 BCE) describes the five vital energies (prana), and concepts of later yoga traditions (such as blood vessels and