I've been reading a lot about the Romans (around 150-50BC) so anything specific to them would be of particular interest, but I'd love to hear about the tactic in general. Thanks :)
Sorry if I don't reply immediately, I won't be online for a few hours but I will absolutely come back read everything asap.
There’s an earlier answer by the mighty u/sunagainstgold
Seems like well poisoning was more threatened/accused than actually done.