"Ancient", a corpus of Sanskrit legends, of ancient Aryan beliefs. The Puranas are considered smriti.
There are a total of 18 major Puranas, all written largely in verse. These texts are said to have been composed much later than the Ramayana and the Mahabharata. The oldest Purana is believed to date back to 300 AD, and the most recent ones to 1300 - 1400 AD. Although they have been composed at different times, all the Puranas seem to have been revised at a later date. This is apparent because all of them state that the total number is 18. The Puranas vary greatly in length: the Skanda Purana is the longest with 81,000 couplets, while the Brahma Purana and Vamana Purana are the shortest with 10,000 couplets each. The total number of couplets in the Puranas collectively is 400,000.
These works consist of short stories and narrations which explain the complicated concepts of the Vedas and the Dharmasutras . These tales are not meant for scholars or researchers, but for lay readers. They are written in the form of a dialogue between an exponent and an inquirer. They teach about religion and morality. However, they also discuss subjects like the origin of insects, and give medical advice for minor ailments.
By definition, a Purana must cover five subjects: the creation of the universe; its destruction and recreation; the principal gods and patriarchs; the reigns of the Manus ; and the history of the Suryavanshi and Chandravanshi kings. However, none of the Puranas match this definition exactly, since none of them covers all five topics.
The 18 major Puranas are divided into three groups, each exalting one member of the Hindu Trinity. Those Puranas in which "rajas" or passion prevails relate chiefly to Brahma.
These are the Brahma Purana, Brahmanda Purana, Brahmavayvarta Purana, Markandeya Purana, Bhavishya Purana, and Vamana Purana.
Those Puranas in which "satva" or purity is the leitmotif are related to Vishnu. These are the Vishnu Purana, Bhagavata Purana, Naradiya Purana, Garuda Purana, Padma Purana and Varaha Purana.
Those in which "tamas" or gloom and ignorance are dominant are related to Shiva. These are the Shiva Purana, Linga Purana, Skanda Purana, Agni Purana, Matsya Purana, and Kurma Purana. Sometimes the Vayu Purana is substituted for the Agni Purana or Shiva Purana.
Of the 18 major Puranas, the Vishnu Purana is the most complete, in that it conforms more than the others to the definition of a Purana. It has also been translated into English. According to some sources, the Markandeya Purana is considered to be the oldest Purana. Other sources state that the Vayu Purana is the oldest. The Bhagavata Purana (also called the Shrimad Bhagavata) is believed to be the most recent and is the most popular.
Apart from these 18 Puranas, there are also 18 Upapuranas or subsidiary Puranas, which were composed after the major ones.
The Puranas are a valuable source from which to trace the development of Hinduism. They mark the next stage in beliefs after the Vedas. Hinduism, as practiced today, is largely inspired by the Puranas.