How do we know what accents people spoke with before the invention of recorded sound?

Question

Most movies and shows set in the past e.g. 1700s, 1600s etc will include some sort of accent. How do we know if people actually spoke in those accents?

Edit: this came up is because I was watching the CBS show Ghosts. In it, there are two ghosts from the American Revolution. The British Revolutionary and the American Revolutionary have distinctly different accents and it made me question how we actually know what they sounded like.

In: 8

Answer 1

We don’t. We have no idea. They just cast British actors because American audiences think British accents sound sophisticated