You could blame the Trebuchet for being the first biological warfare weapon platform. It wasn't unsual for forces to load up the baskets with dead animals, excrement and enemy soldiers as "shot" and send it back over the parapets. IIRC the Romans might have been one of the first militaries who were creative in its use. My money is on the trebuchet - but military weapons from the days of the Roman Imperium were all pretty innovative. OTOH the Mongols developed portable ballistas which coul be used by an individual soldier - probably the first "mortar" in a fashion.

this "BIO warfare" tradition doesn't start with the trebuchet. livy says on several occasions the romans used decomposing carcasses (heads) as ballistae ammunition (for the stone throwing ones). i know the romans used bee hives on more than one occasion, and the crusaders in 1098 used a "perriot" (a mini-trebuchet swung by manpower rather than counter weight) to throw saracen heads over the walls of antioch. but in terms of sheer effectiveness, i still think the carroballistae are the coolest: a battery of eight supporting an infantry attack (on the battlefield or in a siege) would inflict very heavy casualties on an enemy in tight formation, and the pieces were light and rapid firing (relatively, of course), long ranging (some of the better ones had a range of over 880 yards, according Vegetius and Ammianus Marcellinus), accurate, and superb at piercing multiple armoured enemies (the term "catapult" is derived from the greek "kata peltes" or "shield piercers") why i don't like trebuchets is that they are massive and require a long time to set up (though nobody is denying their power). also, unlike the carroballistae, they are useless on the battlefield. and the romans had "hand held" ballistae in the third century ("arcuballistae" or "manuballistae"), all descended from the greek "gastraphetes" ("belly bow") used in the siege of syracuse in the fourth century BC.

IIRC the Romans also used onagers to lob refuse and refuse over the ramparts when sieging. trebuchets are rather massive, but in effect I guess they would be equivalent to todays tactical battlefield rockrets. certainly an onager was more portable

Trebuchets are almost the equivlent of railroad artillery. Massive, fortification smashing support weapons with little tactical battlefield use. Still, they were mighty impressive machines of war.