I had the same problem....almost. The Mongol Khan, Ogadai, was camped outside my artillery towered fortress in northern Russia with an army of the Mongol's best that outnumbered me 6-1, atleast. The first cannon ball fired from behind my ranks hit their Khan, and ONLY their Khan, while all the rest of his men dodged. Then afterward, I held the gate against 1000 Mongol Heavy cavalry with 50 urban militia. talk about luck.