Their influence upon the young tsar was profoundly beneficial, and the period of their administration coincides with the most glorious period of Ivan's reign - the period of the conquest of Kazan and Astrakhan.
In the course of 1551 one of the factions of Kazan offered the whole khanate to the young tsar, and on the 20th of August 1552 he stood before its walls with an army of 150,000 men and 50 guns.
The conquest of Kazan was an epoch-making event in the history of eastern Europe.
Some of Ivan's advisers, including both Sylvester and Adashev, now advised him to make an end of the Crimean khanate, as he had already made an end of the khanates of Kazan and Astrakhan.
Bogdanov, Birds and Mammals of the Black-Earth Region of the Volga Basin (in Russian, Kazan, 1871); Karelin for the southern Urals; Kessler for fishes; Strauch, Die Schlangen des Russ.