<P> In 1247, Balban suppressed a rising of the Chandela Chief of Kalinjar . </P> <P> Balban's military reign also distinguished with his success repelling Mongol army . This could be achieved because his cavalry horses were better suited to Indian climate and naturally bred larger than Mongol's horses . The extreme heat of summer constituted the Mongols' problem in India, as the quotation from Juvaini indicates . Their incursions seem to have been brief, even when not defeated by the forces of Delhi, and to have taken place in winter, because only then was it cool enough for the comfort of the Mongols' horses </P> <P> Since Sultan Nasiruddin did not have a male heir, so after his death, Balban declared himself the Sultan of Delhi . Balban ascended the throne in 1266 at the age of sixty with the title of Sultan Ghyasuddin Balban . </P> <P> During his reign, Balban ruled with an iron fist . He broke up the' Chahalgani', a group of the forty most important nobles in the court . Balban wanted to make sure everyone was loyal to the crown by establishing an efficient espionage system, in the style of the Umayyad Barid . Sultan Balban had a strong and well - organized spy system . Balban placed secret reporters and news - writers in every department . The spies were independent authority only answerable to Sultan . </P>

Which book gives an account of balban period