According to Tacitus, Calgacus (sometimes Calgacos or Galgacus) was a chieftain of the Caledonian Confederacy who fought the Roman army of Gnaeus Julius Agricola at the Battle of Mons Graupius in northern Scotland in AD 83 or 84. His name can be interpreted as Brittonic *calg-ac-os, 'possessing a blade', and is seemingly related to the Gaelic calgach (meaning 'prickly' or 'fierce'). Whether the word is a name or a title is unknown.[1]