Vajrayana is one of the three great doctrinal divisions of Buddhism, along with Theravada and Mahayana. Vajrayana can be understood as tantric Buddhism. Historians debate when Vajrayana first appeared, but it was clearly understood as a separate tradition by the eighth century CE, and most of its major texts were written by the twelfth century. Vajrayana ritual and art are characterized by visualization, deity yoga, wrathful deities, mandalas, mantras, initiations and empowerments (abhisheka), and ritual sexual union. These teachings are transmitted in texts called tantras and sadhanas, as well as through secret instructions (Skt. upadesha) from a teacher. Essentially all Himalayan Buddhist traditions integrate Mahayana and Vajrayana practices.