CMXC

CMXC is the representation of the number 990 in Roman numerals. It uses subtractive notation: CM equals 900 (C placed before M indicates 100 less than 1000), and XC equals 90 (X placed before C indicates 10 less than 100). The two values are added to yield 990.

In practice, CMXC appears in contexts where Roman numerals are used to denote years, monarchs, chapters, or enumerations, such as inscriptions on buildings or clocks. It is the standard modern Roman-numeral form for the year 990. While most contemporary writing uses Arabic numerals, traditional or ceremonial contexts may still employ CMXC.

Notes on usage: The formation CMXC is consistent with common subtractive rules for Roman numerals, which avoid subtractive pairs like IC or IM. For adjacent numbers in the 900s and 990s, CMXC is typically preferred; 991 would be CMXCI, and 999 would be CMXCIX.

CMXC remains a valid and widely recognized representation of 990 in Roman numerals, preserving compatibility with historical inscriptions and systems that continue to employ the numeral alphabet.