Sci fi movie experts

Hello!

I have just stumbled across your website/service and am wondering if perhaps you might help me solve a mystery that I have been trying to conclude for about 10-15years!

This movie that I am asking about was I believe made in the 80's..pretty sure it wasn't the 70s...but alas, all I can remember is the movie is about a fortress/a tower that disspears and reappears during the course of the movie and along with this tower is some sort of army of evil creatures that are normally riding on horse back with spears and they seem hell bent on killing everybody, humans etc

The beginning of the movie is a wedding ceremony of some sort where two people are clasping hands over a sort of font or well and a magical flame appears that I'm guessing symbolises their union and then..all of of a sudden there's an attach by these evil guys on horseback...I remember that when they (the evil dudes) get killed a worm/snake like thing escapes from there humanoid looks bodies and tries to bury itself in the ground...

After that its very much a blur but in the movie there's a group of people/survivors that are trying to seek out the castle and get inside and kill whoever is responsible...its like a black tower/castle/fortress...but that's about it...I just remember it appears and reappears in different places and wherever it goes an army of evil guys on horseback attack people and villages...

Would love to watch it again..do you think you could help me?!?! If you have an idea of what the movie is called I'd be so grateful.

Thank you for all your help and efforts whatever you come up with, I appreciate it.

All the best, 'stgeorge041982 (from very very cold and wintery England) :-)