The origins of Yoga have been speculated to date back to pre-vedic Indian traditions, but most likely developed around the sixth and fifth centuries BCE, in the same ascetic circles as the early sramana movements. The earliest accounts of yoga-practices are in the Buddhist Nikayas. Parallel developments were recorded around 400 CE in the Yoga Sutras of Patanjali, which combines pre–philosophical speculations and diverse ascetic practices of the first millennium BCE with Samkhya-philosophy. Hatha yoga emerged from tantra by the turn of the first millennium.