DCLXI is a Roman numeral that represents the number 661. In the Roman numeral system, letters are combined to signify values, where "D" stands for 500, "C" for 100, "L" for 50, and "XI" for 11. When added together, these values total 661. Roman numerals are often used in various contexts, such as in the naming of monarchs and popes, or to denote the year of publication in books. Understanding Roman numerals can be helpful in reading historical texts or interpreting dates in classical architecture, such as those found in ancient Rome.