Cavalry go through the gate if grouped, I have used my cavalry battering rams many times to crash through enemy formations contesting breaches. What happens is the cavalry group halts in front of the gate quite a while, in line, in column, whatever, then one unit by one unit they will pass through the gate. However, second unit comes so close on the heels of the first that you end up with a traffic jam anyway. >.<. I wish I knew what number in what textfile to change so that the cavalry would wait longer before passing through so the group retains unit coherence.