In this handout photo released on Thursday, Oct. 5, 2023, Senior Researcher at the National Museum of Denmark Mads Dengso Jessen holds a window glass fragment from the Viking Age, in Copenhagen, Denmark, Sept. 8, 2023. Over the past 25 years, archaeologists have found glass fragments in six excavations in southern Sweden, Denmark and northern Germany and have analyzed fragments of glass panes to reach the conclusion: Vikings had windows with glass-panes. (John Fhær Engedal Nissen/The National Museum of Denmark via AP)