According to the Vishnu Purana (3.2.18, 3.3.4 etc.) the original Veda was divided into four parts, and further fragmented into numerous shakhas, by Vishnu in the form of Vyasa, in the Dvapara Yuga; the Vayu Purana (section 60) recounts a similar division by Vyasa, at the urging of Brahma. The Bhagavata Purana (12.6.37) traces the origin of the primeval Veda to the syllable aum, and says that it was divided into four at the start of Dvapara Yuga, because men had declined in age, virtue and understanding. Another view is that the original veda was called Pranava Veda and is attributed to Brahmarishi Mayan, the great architect. This Veda is held by Vaastu Vedic Trust. In a differing account, the Bhagavata Purana (9.14.43) attributes the division of the primeval veda (om) into three parts to the monarch Pururavas at the beginning of Treta Yuga.