Most programs incorporate primary source material, first-hand accounts, dramatic reenactments, and computer-generated imagery (CGI) to tell the story.
In the case of original British episodes, PBS re-edited, re-branded and finally re-narrated them with various American voice artists.
[1] PBS description: "Scientists seek to uncover celebrated mysteries of the past in this occasional British series."
Episode topics (Which are listed in different order on PBS) have included the Titanic, D-Day, the Shroud of Turin, the Salem Witch Trials, Blackbeard's lost ship, and the first English translations of the Bible.
The PBS series premiered on May 15, 2000, airing four programs in three days (the first episode, concerning the Extreme weather events of 535–536, was a two-parter).