Cold siege weapons have a chance to drop in Cyrodiil dolmens.
Cold fire siege weapons can usually one-shot low health players in non-cp campaigns and cause massive damage in the cp-enabled campaigns. Tip: Operate two at one time.
The best cold siege weapon is the Cold Fire Ballista but be sure to repair them frequently as they degrade quite fast. Tip: Don’t operate two at a time if you can’t afford the losses should one or both get destroyed.
They’re also expensive in guild stores going at around 5000 gold.