Well, they had Heretic, Heretic: Shadow of the Serpent Riders (which was the full game and an extra two episodes), then came along Hexen. Hexen does not follow the same story that Heretic does, so it is called Hexen. Then we have Hexen: Deathkings of the Dark Citadel , which was an expansion pack that I had lost. We also have Hexen 2, and then Hexen 2: Portal of Praevus.
Then Heretic 2 was released, which has no relation to the Hexen serie of games.
Yeah, one of the best mods of all time was Siege, a mod for Hexen 2. There would be two teams and one would have catapults to launch barrels at the wall with. They could swim in a moat but must beware of the fish that bite. There were a lot of things in that mod; so many things, that it could never get boring. However, it was not played forever, and before I had noticed, barely anyone was playing.