[quote=@Nerevarine]
[@Willy Vereb]

I figured we would be starting around the 12th century, with guns being a mild rarity and the production of more advanced guns being a lost art. 

Biological warfare and use of nuclclear waste fits right in with a pseudo medieval setting
[/quote]

Actually nuclear waste would be as harmful, if not more to the attackers on the given basis what'll be thrown won't be in well contained units anymore, if they can even get to it. A lot of nuclear waste emits enough radiation to make someone immediately cripplingly physically ill and disoriented (about 1 sievert).

Plus it goes rightly against what makes warfare an incentive, taking land. If you're throwing around canisters full of nuclear coolant waste you're easily polluting the soil you want to take over. That is if anything can actually leave the catapult (rusty metal drums don't tend to fair well when forced to go through sudden acceleration with a trebuchet or catapult, it'll be likely they explode as you soon as they're thrown).