From Germanic 'beraht' meaning 'bright, famous'; a continental form of Bertha.
Berta is an ancient Germanic name in its own right, not merely a shortening — it descends directly from the Old High German beraht, meaning "bright" or "famous," and stands as a root name from which Alberto, Roberta, Herbert, and dozens of other compounds grew. In early medieval Europe, Berta was a name of queens: Bertha of Kent, who married the pagan King Ethelbert of Kent in the late 6th century and is credited with preparing England for the Augustinian mission and the eventual conversion of the Anglo-Saxons, bore an early form of it. Charlemagne's mother, Bertrada, was called Berta in the chronicles.
Brightness and nobility followed the name across the continent. The name took a complicated cultural turn in 1914 when the massive German siege howitzer used in World War I was nicknamed "Dicke Bertha" (Fat Bertha) by German soldiers, reportedly after Bertha Krupp, heiress to the Krupp armaments empire. This association haunted the name in English-speaking countries for decades, contributing to its mid-20th-century decline in Britain and America even as it remained perfectly respectable in Germany, Austria, Italy, and Spain, where Berta and Bertha maintained steady use.
In 19th and early 20th century America, Berta was a natural choice in German-immigrant communities and among families who wanted a solid, dignified name without excessive ornamentation. Today it reads as quietly distinguished — carrying the same root brightness as Roberta or Alberta but in leaner, more directform. Its Italian and Spanish cognate forms have helped keep the sound alive internationally, and the growing appetite for Victorian-era names suggests Berta's moment of rediscovery may not be far off.