Historical Science Fiction

Poul Anderson wrote not only historical fiction and historical fantasy but also historical science fiction (sf). Time travel, immortality and alien contact are sf. Therefore, any of these three subjects in a historical period is historical sf. In fact, Anderson wrote:

one novel about immortals living through various historical periods into the present and on into the future; 
one novel about alien contact in a historical period;
several volumes about time travelers visiting different historical periods as well as various future periods.

Hanno the immortal was born in Tyre when Hiram was its king and Manson Everard of the Time Patrol met Hiram. However, these were in different timelines. The future into which Hanno survives is not the future of the timeline guarded by the Patrol. But other works by Anderson allow for multiple timelines. Thus, Anderson's complete works display both immense imagination and immense historical knowledge.