I love period films, I think some of my favourites are:

A Man for All Seasons, about Thomas More and Henry VIII.

Stage Beauty, which is about actors in the court of Charles II of England.

Master and Commander: Far Side of the World, an age of sail war movie.

A Dangerous Man, about T. E. Lawrence and Emir Feisal at the Paris Peace Conference.

Design for Living, OT3 Noel Coward comedy.

Love and Friendship, a Lady Susan adaptation with a fun ending.

Twelve O'Clock High, about the US bomber command in WWII.

The Guns of Navarone, WWII action movie, mostly because it's immensely slashy.

Man in the Grey Flannel Suit, about processing war trauma in the 1950s.