According to Axel Michaels, the first inscriptional evidence of the practice is from Nepal in 464 CE, and in India from 510 CE. The early evidence suggests that widow-burning practice was seldom carried out in the general population. Centuries later, instances of "sati" began to be marked by inscribed memorial stones called Sati stones. According to J.C. Harle, the medieval memorial stones appear in two forms – "viragal" (hero stone) and "satigal" (sati stone), each to memorialize something different. Both of these are found in many regions of India, but "rarely if ever earlier in date than the 8th or 9th century". Numerous memorial "sati" stones appear 11th-century onwards, states Michaels, and the largest collections are found in Rajasthan. There have been few instances of sati in the Chola Empire in South India. Vanavan Mahadevi, the mother of Rajaraja Chola I (10th century) and Viramahadevi the queen of Rajendra Chola I (11th century) both committed Sati upon their husband's death by ascending the pyre.