Just east of the San Francisco Bay Area are the Berkeley Hills Walls--remnants of a massive, stone wall that stretches a distance of over fifty miles, in Season 3, Episode 7, "Marco Polo Discovers America." #AmericaUnearthed Subscribe for more from America Unearthed and other great The HISTORY Channel shows: histv.co/SubscribeHistoryYT Find out more about the show and watch full episodes on our site: www.history.com/shows/ Check out exclusive The HISTORY Channel content: History Newsletter - histv.co/newsletter Website - histv.co/History Facebook - histv.co/Facebook Twitter - histv.co/Twitter In "America Unearthed," host Scott Wolter uses hard science and intuitive theories to explain the most mysterious artifacts and sites in America. HISTORY® is the leading destination for award-winning original series and specials that connect viewers with history in an informative, immersive, and entertaining manner across all platforms. The network's all-original programming slate features a roster of hit series, premium documentaries, and scripted event programming.