Alright, I'm getting frustrated.

I am playing as Russia and I am loading up some of my volatile cities in central Europe with a militia army consisting of five archer militia units (along with others). I get sieged and assaulted about every other turn in the current game, but at first I figured it would be easy to light up the siege rams with five full salvos of flaming arrows raining down.

Wrong.

I rarely, if ever, can get sieqe equipment to catch on fire, even in clear weather. Does anyone have more success with this? Is it a function of missile damage, and my archers just aren't powerful enough?