The Historian of science George Sarton called him "one of the greatest Scientists of his race and the greatest of his time." Brahmagupta's mathematical advances were carried on further by Bhāskara II, a lineal descendant in Ujjain, who described Brahmagupta as the *ganaka-chakra-chudamani* (the GEM of the circle of mathematicians). Prithudaka Svamin wrote commentaries on both of his works, rendering difficult verses into simpler language and adding illustrations. Lalla and Bhattotpala in the 8th and 9th centuries wrote commentaries on the *Khanda-khadyaka*. Further commentaries continued to be written into the 12th century.