Half the time with city fortifications it "forgets" them. Eg Florida and Netherlands. I had to fight several dozen siege defences when the Cherokees attacked with pitifully inadequate forces (2 inf+6 cav vs 6 inf) but the autocalc had me getting massacred, when I normally lose all of 12 guys. Such a waste of time, I could only play a few turns before getting frustrated and quitting.