Cārvāka is classified as a "nāstika" ("heterodox") system; it is not included among the six schools of Hinduism generally regarded as orthodox. It is noteworthy as evidence of a materialistic movement within Hinduism. Our understanding of Cārvāka philosophy is fragmentary, based largely on criticism of the ideas by other schools, and it is no longer a living tradition. Other Indian philosophies generally regarded as atheistic include Samkhya and Mimāṃsā. Two of Hinduism's most revered "epics", the Mahabharata and Ramayana were compositions of this period. Devotion to particular deities was reflected from the composition of texts composed to their worship. For example, the "Ganapati Purana" was written for devotion to Ganapati (or Ganesh). Popular deities of this era were Shiva, Vishnu, Durga, Surya, Skanda, and Ganesh (including the forms/incarnations of these deities). In the latter Vedantic period, several texts were also composed as summaries/attachments to the Upanishads. These texts collectively called as Puranas allowed for a divine and mythical interpretation of the world, not unlike the ancient Hellenic or Roman religions. Legends and epics with a multitude of gods and goddesses with human-like characteristics were composed. The Gupta period marked a watershed of Indian culture: the Guptas performed Vedic sacrifices to legitimize their rule, but they also patronized Buddhism, which continued to provide an alternative to Brahmanical orthodoxy. Buddhism continued to have a significant presence in some regions of India until the 12th century. There were several Buddhistic kings who worshiped Vishnu, such as the Gupta Empire, Pala Empire, Malla Empire, Somavanshi, and Satavahana. Buddhism survived followed by Hindus. Tantrism originated in the early centuries CE and developed into a fully articulated tradition by the end of the Gupta period. According to Michaels this was the "Golden Age of Hinduism" (c. 320–650 CE), which flourished during the Gupta Empire (320 to 550 CE) until the fall of the Harsha Empire (606 to 647 CE). During this period, power was centralised, along with a growth of far distance trade, standardizarion of legal procedures, and general spread of literacy. Mahayana Buddhism flourished, but the orthodox Brahmana culture began to be rejuvenated by the patronage of the Gupta Dynasty.