The Past

Approximately thirty volumes by Poul Anderson address the past in different ways.

Prehistoric: Conan the Rebel.
Pre-Christian: The Dancer from Atlantis; The Golden Slave.
The Roman Empire: the King of Ys tetralogy, with Karen Anderson.
The Dark Ages: The Broken Sword; The Demon of Scattery.
Vikings: War Of The Gods; Hrolf Kraki's Saga; Mother of Kings; the Last Viking trilogy.
The fourteenth century: Rogue Sword; The Merman's Children; The High Crusade.
Various periods: The Boat of a Million Years; Past Times; The Corridors of Time; the Time Patrol series (either two or four volumes); enough short stories for a collection.
Alternative histories: Three Hearts and Three Lions; Operation Chaos; Operation Luna; A Midsummer Tempest; a collection.

Maybe five genres:

heroic fantasy;
historical fantasy;
historical fiction;
science fiction;
science fantasy (?)

I am not sure about that fifth category but maybe the first edition of The Broken Sword with its scientific rationales for fantasy elements qualifies? I have also coined the term "hard fantasy" (based on "hard sf"),  meaning not fiction with scientifically rationalised fantasy premises but fiction whose fantasy premises are, like the technological premises of hard sf, developed with logical precision.

Anderson's hard sf addresses many futures in more than thirty volumes. His novels include one contemporary fantasy and three detective novels.