Yoga's history has many places of obscurity and uncertainty due to it's oral transmission of sacred texts and the secretive nature of it's teachings. It's roots can be traced back to 5,000 years ago, although some researchers think Yoga may be up to 10,000 years old. The Classical period of Yoga is defined by Patanjali's Yoga Sutras, the first systematic presentation of Yoga. Written sometime in the second century this these texts describe the path of Raja Yoga, often called 'classical Yoga'. Patanjali organized the practice of Yoga into an eight limbed path, containing the steps and stages towards obtaining Samadhi or enlightenment. Patanjali is often considered the father of Yoga and his Yoga Sutras still strongly influence most styles of modern Yoga.