Historians speculate on what could possibly be hidden in the cornerstone of the White House. See more in this clip from Season 4, "Secrets of the Founding Fathers."

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From the producers of Ancient Aliens and The Curse of Oak Island comes The UnXplained, a one-hour, non-fiction series that explores the world's most fascinating, strange and inexplicable mysteries. Hosted and executive produced by Golden Globe and Emmy Award-winning actor William Shatner (Star Trek, Boston Legal) each episode will feature compelling contributions from scientists, historians, witnesses and experiencers-each seeking to shed light on how the seemingly impossible actually can happen.

The HISTORY® Channel, a division of A+E Networks, is the premier destination for historical storytelling. From best-in-class documentary events, to a signature slate of industry leading nonfiction series and premium fact-based scripted programming, The HISTORY® Channel serves as the most trustworthy source of informational entertainment in media. The HISTORY® channel has been named the #1 U.S. TV network in buzz for seven consecutive years by YouGov BrandIndex, and a top favorite TV network by Beta Research Corporation. For a deeper dive, visit history.com or follow @history on Instagram, Twitter, Facebook, YouTube and TikTok. For additional press materials visit the A+E Networks Press Center at http://press.aenetworks.com.