CDXXIII

CDXXIII is a Roman numeral that encodes the number 423. The numeral is formed with subtractive and additive principles: C before D yields 400, and XXIII adds 23, giving 423 in total.

In historical contexts, CDXXIII would designate the year 423 CE in the Julian calendar. That era corresponds to the early fifth century, a time of political transition within the Western Roman Empire; however, the numeral itself does not imply any specific event.

In modern usage, CDXXIII can appear in inscriptions, catalogs, or enumerations that employ Roman numerals—for example as a chapter or volume designation, a film or product subtitle, or a placename marker. It is not restricted to a single discipline and commonly serves as a stylistic or conventional numbering choice.

The notation CDXXIII is one example of subtractive notation in Roman numerals, where symbols placed before larger values reduce the value (C before D to make 400). Other common numerals include I, V, X, L, C, D, and M, and their combinations follow similar rules.