Roman Numerals are numerical symbols formed with the Roman letters I, V, X, L, C, D, and M, representing respectively the numbers 1, 5, 10, 50, 100, 500, and 1000, used by the ancient Romans. If interested, you can visit here to learn: How to read and write Roman Numerals.

A Synopsis on the History of Roman Numerals
Roman numerals were the standard numbering system and method of Arithmetic in Ancient Rome and Europe. Rome being the world leader at the time was dominant and very active in trade and commerce and needed a way to indicate numbers to carry out their daily business (finances) and to calculate their taxes. Also, being a modernized society in their era there was a demand and need to improve their architectual capabilities in building roads, bridges, fortresses, temples, stadiums, ships etc, as they expanded and their society became more sophisticated. It was then that Roman scholars invented numerical characters known as Roman Numerals as a standard numbering system.

This system was in use up to about 900 AD, when the Hindu's originated the Arabic Numbering System ( Arabic numerals). Arabic numerals (also called Hindu numerals or Indian numerals or Western numerals ) are the most common set of symbols used to represent numbers and is also the one we use today. Arabic numerals is made up of the characters 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 and in general European use since the 12th century. Unlike the Arabic numerals, Roman numerals didn't have a symbol for zero (0) and as a result, because the concept of zero did not exist, the numeral placement was sometimes based on subtraction rather than addition. The largest number that could be represented by the roman numerals system using their rules was 4,999.

Traditional Use of Roman Numerals
Traditionally roman numerals were used to indicate the order of family offspring of the same name ( For example, II was used instead of Jr., III for the third, and IV for the fourth and so on) and also if the same surname were used by church leaders (Popes) and kings (whether or not by off spring) this numbering system was used to indicate that order . In England, kings used this system of naming their kings that carried the same surname. The Romans in their time conquered many different countries and England was one of such countries. After conquering England, Romans settled there, where the English and other people would adapt the number system used by Romans. This is why for example kings of England like King Henry the 1st written as King I (pronounced: as King Henry the first) or king Henry the 8th written as Henry VIII (pronounced: King Henry the eight) used these roman numerals in their name. This is saying, using the latter as an example, that King Henry VIII was the 8th person to be King of England with the name "Henry". The same can be explained for Queen Elizabeth the 1st ( Elizabeth I) and Queen Elizabeth the 2nd (Elizabeth II), pronounced: Queen Elizabeth the Second, the present queen of England. If there should be another queen Elizabeth, she would be named Queen Elizabeth the third written as Queen Elizabeth III and would pronounced Queen Elizabeth the third.

Roman Numerals were also used for as dating on cornerstones of buildings showing origin of a building, statutes, headstones, ships (e.g. Queen Elizabeth II), books publication such as in chapter titles, volume of book series, appendices and so on.

The Use of Roman Numerals Today

Today the Roman Numerals are used as:
i.) Numbers in publishing and media industries for copyright dates,

ii) In books such as; pagination of preliminary pages (in lower case), appendices, chapter headings and title pages to show dates of publication.

iii) Numerical labels in lower case in the listing of written content (e.g. i, ii, iii, iv etc.),

iv) A part number to Arabic numbers (0, 1, 2, 3, 4, 5, 6, 7, 8, 9) in sub-list {1. (i), 1. (ii), 1. (iii) …2. (i), 2 (ii)… and alphabet sub-listing {A (i), A (ii), B (i), B (ii)…..etc.}.

v) Clocks

vi) Watches,

vii) to indicate the anniversary of Super Bowl games in the US,

viii) headstones,

viiii) cornerstones of some building signifying date of construction etc.

x) family offspring of the same surname name usually after the third consecutive use of the surname i.e. after using the term Sr. and Jr.

xi) the naming of church leaders such as the Pope of the catholic church that may use the same name of previous Popes.

xii) the numbering of movie sequels

Related Article:
How to read and write Roman Numerals