 Complete the following phrase:  In November 1237 Batu Khan sent his envoys to the court of Yuri II of Vladimir-Suzdal and demanded his allegiance. When Yuri refused to surrender the Mongols besieged Ryazan. After six days of bloody battle, the city was totally annihilated and never restored to its former glory. Alarmed by the news, Yuri II sent his sons to detain the horde, but they were soundly defeated. Having burnt Kolomna and Moscow, the horde laid siege to the capital of Vladimir-Suzdal on 4 February 1238. Three days later the city was taken and burnt to the ground. The royal family perished in the fire, while the grand prince hastily retreated northward. Crossing the Volga, he mustered a new army, which was totally exterminated by the Mongols 