Bhakti can be used of either tradition of Hindu devotionalism, Shaivaism or Vaishnavism. While bhakti as designating a religious path is already a central concept in the Bhagavad Gita, it rises to importance in the medieval history of Hinduism, where the Bhakti movement saw a rapid growth of bhakti beginning in Southern India with the Vaisnava Alvars (6th-9th century CE) and Saiva Nayanars (5th-10th century CE), who spread bhakti poetry and devotion throughout India by the 12th-18th century CE.