The word "yoga" means union, specifically the union of the individual soul with the cosmic soul, or the union of kriya kundalini shakthi with Yogi Shiva, the cosmic Godhead. This union also symbolizes the meeting of people from different walks of life and the convergence of all world religions. This scientific art is called yoga. Before the Aryans arrived with their spoken language of Sanskrit, the Dravidians in India practiced this scientific art, as evidenced by archaeological remains of the Indus Valley civilization in Mohenjo-Daro, Harappa, and other southern sites, where yoga postures and Shiva Lingams have been discovered. The most ancient religion is Saivism, where Yogi Shiva is worshipped through yoga.
When the Aryans invaded India, they integrated into the vast ocean of Hinduism and Saivism. They developed a script for Sanskrit and learned yoga from the Dravidian Tamil race with the help of Tamil yoga Siddhar Patanjali. The Bhagavad-Gita (chap. IV.V.1,2) mentions that Jothimayavivashvavarna taught yoga to Manu, also called Moses, who established the rules of dharma. Manu then taught this yoga to King Ikshavaku, the founder of the Solar Dynasty, and for generations, yoga was practiced by the Raja Rishis (Royal sages).
Sri Aurobindo explained that different countries flourished and declined over time, like the Roman Empire. During their golden ages, yoga was openly practiced by many people, such as Raja Rishi Janaka in the Treta Yuga of Sri Rama. However, India’s yogic tradition has remained continuous.
As the golden age is followed by the dark age of ignorance and materialism, to prevent the misuse of yoga, the Siddhars imposed conditions for learning it. When yogic knowledge was in danger of being lost, avatars and Siddhars were born to revive it.
In the Dvapara Yuga, Lord Krishna taught this scientific art to Arjuna (Bhagavad-Gita IV, 29; V, 27 & 28). Later, the great Tamil sage Patanjali summarized this Kriya Raja Yoga into hymns, now one of the six major systems of philosophy in Hinduism. Elijah, Jesus, and other prophets practiced yoga with modifications.
In modern times, as India entered a new golden age or Satya Yuga, spiritual giants like Ramakrishna Paramahamsa, Sri Aurobindo, Sage Ramana Maharishi, Mahatma Gandhi, and Kriya Babaji revived and practiced yoga. Kriya Babaji Nagaraj, a key figure in the Tamil Eighteen Siddhars' tradition, named this science Kriya Yoga.