The Roman numeral "DCLXXXVI" represents the number 686. In this numeral, "D" stands for 500, "C" for 100, "L" for 50, and "X" for 10. The combination of these symbols adds up to 686, as the letters are summed according to their values. Roman numerals are a numeral system originating from ancient Rome. They use combinations of letters from the Latin alphabet to signify values. This system was widely used throughout the Roman Empire and is still seen today in various contexts, such as on clock faces and in the naming of monarchs and popes.