Explanation:

• The Kumbh at Sangam city Prayagraj, as Allahabad is now known, dates back to a hoary past, whose first mention of was made some 2,000 years ago by the Chinese traveler Hsuan Tsang who visited India during the reign on King Harshvardhana.
• Based on a complex astrological calculation, the alignment of the stars determines the time and place of the Kumbh' in one of the following four river-sites: Haridwar, Prayagraj, Nasik and Ujjain.