CXXXVIII is the Roman numeral representation for the number 138. Roman numerals are a numeral system originating from ancient Rome, using combinations of letters from the Latin alphabet. In this system, "C" stands for 100, "X" for 10, and "VIII" for 8, which together add up to 138. The number 138 can be found in various contexts, such as in mathematics, history, and even in literature. For example, it is the atomic number of the element barium, a chemical element used in various applications, including medical imaging. Additionally, 138 can represent years in history, such as the year 138 AD, which was notable for various events in the Roman Empire.