Roman numeral dating
The calendar originally consisted of hollow months that were 29 days long or full months that had 30 days.
They are also used in the IUPAC nomenclature of inorganic chemistry, for the oxidation number of cations which can take on several different positive charges.
They are also used for naming phases of polymorphic crystals, such as ice.
An extra month was added to the calendar in some years to make up for the lack of days in a year.
The numeric system represented by Roman numerals originated in ancient Rome and remained the usual way of writing numbers throughout Europe well into the Late Middle Ages.
The addition of January and February meant that some of the months' names no longer agreed with their position in the calendar (September - December).
In particular, army corps are often numbered using Roman numerals (for example the American XVIII Airborne Corps or the WW2-era German III Panzerkorps) with Hindu-Arabic numerals being used for divisions and armies.In music, Roman numerals are used in several contexts: (See the sections below on "zero" and "fractions".) In photography, Roman numerals (with zero) are used to denote varying levels of brightness when using the Zone System.
Usage in ancient Rome varied greatly and remained inconsistent in medieval and modern times. One hypothesis is that the Etrusco-Roman numerals actually derive from notches on tally sticks, which continued to be used by Italian and Dalmatian shepherds into the 19th century., the initial of Mille (the Latin word for "thousand").Roman numerals, however, proved very persistent, remaining in common use in the West well into the 14th and 15th centuries, even in accounting and other business records (where the actual calculations would have been made using an abacus).Replacement by their more convenient "Arabic" equivalents was quite gradual, and Roman numerals are still used today in certain contexts. In chemistry, Roman numerals are often used to denote the groups of the periodic table.King Numa Pompilius reformed the calendar around 700 BCE by shortening the 30-day months to 29 days and adding the 29-day month of January (Ianuarius) and the 28-day month of February (Februarius) to the original 10 months.This increased the year's length to 354 or 355 days.The ancient Roman calendar, or “pre-Julian” calendar, is believed to have been a lunar calendar.