I had 7 or 8 battles defending my capitol in which NONE of the attackers EVER moved.  All other battles are normal.  The only thing I can think of is that some baddie cast both "frozen bones" and "incinerate city" on my cap.  One of those must paralyze attackers (?)

In one of those battles I cast "gift of iron" and all my city militia dropped dead !   Some gift

Also, in about half those battles no city militia even showed up.  Seemed to alternate between normal and none.     Maybe they were afraid to show up because they thought I might cast the wrong spell again  ?