The Deadliest Ancient Invention Wasn’t a Sword: How Mail Armor Saved Lives for Centuries Mail armor, often called chain mail, was one of the most successful defensive inventions in military history. Instead of one solid plate, it used thousands of interlinked metal rings to create flexible protection against cuts, slashes, and some glancing blows. Britannica notes that early forms of mail were used by late Roman times and may have originated in Asia, while the Met says mail was the predominant a