The Roman numeral "DCCLXXX" represents the number 780. In this numeral, "D" stands for 500, "CC" represents 200 (100 each), "L" is 50, and "XXX" equals 30 (10 each). When combined, these values add up to 780. Roman numerals are a numeral system originating from ancient Rome. They use combinations of letters from the Latin alphabet, including I, V, X, L, C, D, and M. This system was widely used throughout the Roman Empire and is still seen today in various contexts, such as clock faces and book chapters.