sources such as the Majjhima Nikāya mention meditation; the Aṅguttara Nikāya describes jhāyins (meditators) who resemble early Hindu descriptions of muni, the Kesin and meditating ascetics, but the meditation practices are not called "yoga" in these texts. The earliest known discussions of yoga in Buddhist literature, as understood in a modern context, are from the later Buddhist Yogācāra and Theravada schools. Jain meditation is a yoga system which predated the Buddhist school. Since Jain sources are later than Buddhist ones, however, it is difficult to distinguish between the early Jain school and elements derived from other schools. Most of the other contemporary yoga systems alluded to in the Upanishads and some Buddhist texts have been lost. Upanishads The Upanishads, composed in the late Vedic period, contain the first references to practices recognizable as classical yoga. The first known appearance of the word "yoga" in the modern sense is in the Katha Upanishad (probably composed between the fifth and third centuries BCE), where it is defined as steady control of the senses whichwith cessation of mental activityleads to a supreme state. The Katha Upanishad integrates the monism of the early Upanishads with concepts of samkhya and yoga. It defines levels of existence by their proximity to one's innermost being. Yoga is viewed as a process of interiorization, or ascent of consciousness. The upanishad is the earliest literary work which highlights the fundamentals of yoga. According to White, The hymns in book two of the Shvetashvatara Upanishad (another late-first-millennium BCE text) describe a procedure in which the body is upright, the breath is restrained and the mind is meditatively focused, preferably in a cave or a place that is simple and quiet. The Maitrayaniya Upanishad, probably composed later than the Katha and Shvetashvatara Upanishads but before the Yoga Sutras of Patanjali, mentions a sixfold yoga method: breath control, introspective withdrawal of the senses, meditation (dhyana), mental concentration, logic and reasoning, and spiritual union. In addition to discussions in the Principal Upanishads, the twenty Yoga Upanishads and related texts (such as Yoga Vasistha, composed between the sixth and 14th centuries CE) discuss yoga methods. Macedonian texts Alexander the Great reached India in the 4th century BCE. In addition to his army, he brought Greek academics who wrote memoirs about its geography, people, and customs. One of Alexander's companions was Onesicritus (quoted in Book 15, Sections 63–65 by Strabo in his Geography), who describes