Medieval. Crusader. Viking. Caribbean Pirate. Colonial/Revolutionary War. Civil War. Wild West. Victorian. Steampunk. Great War. WW2.
Shooting a period piece can be expensive and beyond the budget of most small scale filmmakers. Sure, you can wardrobe up a couple of actors. And, maybe, come up with a neutral location that could pass for anywhere, anytime.
But if you want to “wow” your audience, it would be nice to have a bunch of costumed players and period encampments in the background!