The Roman numeral "DCCCXLV" represents the number 845. In this numeral, "D" stands for 500, "CCC" represents 300 (100 each for three "C"s), "XL" indicates 40 (50 minus 10), and "V" signifies 5. When combined, these values total 845. Roman numerals are a numeral system originating from ancient Rome. They use combinations of letters from the Latin alphabet, specifically 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.