For the most part, we've not seen much of naval battles in TES. We've heard stories of naval battles, such as the Maormer fleet being destroyed by the Psijics, and clashes on the Niben River during the Great War, but we've not actually seen much of it, and most ships we've seen little in the ways of naval weaponry.

Then Skyrim came along and we got to see what warships in Tamriel are capable of. In http://www.uesp.net/wiki/Skyrim:Rise_in_the_East, the East Empire Company subjects Japhet's Folly to some sort of bombardment. A rather nasty from of bombardment. Given the rarity of mages in Skyrim and the arcing projectiles, I'm fairly certain it wasn't magic. We know that cannons exist in TES but we've not heard of or actually seen them outside Hammerfell. We also know that other forms of artillery exist, but have not been alluded to outside of Cyrus' sword-meeting with Tiber Septim.

So, what does everyone think? What sort of weapons do you guys think the East Empire Company was using to level Japhet's Folly? Because if a trading company (albeit a very powerful and influential one) is able to acquire such weapons, I imagine any major power probably could.

Could be cannons, could be ballistas and catapults. And given the angle they were coming in at, I'd say the later.

As was mentioned to me when I brought up the subject last, cannonballs don't explode, or apparently arc like that. I honestly am not sure though, as I'm still not totally sold on it not being artillery of some kind. It could be that the soldiers present were in fact battlemages volleying spells at the base once it came into view.