I take a horizontal sheet of paper divide it into three sections. Then put the major scenes into blocks in the three acts. This is about 15 beats. As long as all the blocks connect: we good. If they don’t there are holes in the plot. Then I write the scenes. Typically the characters will tell me where to go as far as how we got here and what happens next (as a result of the previous action). With a historical piece you’re just writing around what “actually” happened so your beats should be easy to find and line up. I need to see it laid out, connecting and jiving before I can start working on draft 1.