The zone takes its name from a curious event that occurred to Emperor Constantine the Great, when, during the Battle of Saxa Rubra (312), the "labarum" fell out of his hand. The " labarum" was a military standard that displayed the "Chi-Rho" symbol, a christogram formed from the first two Greek letters of the word "Christ" (, or Χριστός) — "Chi" (χ) and "Rho" (ρ).