I can't say for sure, but I performed bombing with more then 100 ballista elephants and there was no change in the defense of a city I attacked, so it does not look like this. I'm afraid, that at least a part of the problem may involve the python code, so it can take more time fix. @Thunderbrd, I have a feeling, that there may be two problems. One may be, the evaluation is done on integer numbers not on floating-point, so if a bombing strength would be for example 0.4, it will be in this case 0. The second thing is, I've noticed, that strength of bombings is downgraded by some factor. When I bombed one city with the defense something between 100-200%, ballista elephants was making some damage (1 or 2% if I remember correctly). When after few turns, I bombed a city with ~240%, they did nothing. But this is certainly not the matter of the protection against defense reduction, as siege rams performed still a damage. The second can explain everything, if the factor is additive, not multiplicative, as the elephants may have bombing strength reduced to 0 then. BTW, isn't it, that someone is too eager in implementing new formulas here?