Like The Seventh Seal it is set during the plague years, in the 14th century. It's a gruesome, nihilistic film directed and written by creators of previous low-budget Euro horrors such as Severance and Wilderness.
The plot is that Sean Bean and some Christian mercenaries, plus a young monk, go to find a village deep in the marshes which has not been affected by the plague, and where they are not Christian. Either they are just a luckily isolated settlement, or they are in league with Satan. The answer to that is the resolution to the film so I won't say.
My sympathies, and I suspect this was the intention, tended to be with the villagers, and in this respect it's a bit like The Wicker Man, but without quite the heft of that film. It's a competently told story, with good production and acting, and it didn't lose its way or crap out. It seemed a little futile and bloody to me. It's got a lot of murdering and torturing in it, and everyone is grubby all the time like in Monty Python and the Holy Grail.