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. Numbers in this system are represented by combinations of letters from the Latin alphabet. The use of Roman numerals continued long after the decline of the Roman Empire. From the 14th century on, Roman numerals began to be replaced in most contexts by the more convenient Hindu-Arabic numerals; however, this process was gradual, and the use of Roman numerals persists in some minor applications to this day.
The numbers 1 to 10 are usually expressed in Roman numerals as follows:
I, II, III, IV, V, VI, VII, VIII, IX, X.
Numbers are formed by combining symbols and adding the values, so II is two (two ones) and XIII is thirteen (a ten and three ones). Because each numeral has a fixed value rather than representing multiples of ten, one hundred and so on, according to position, there is no need for “place keeping” zeros, as in numbers like 207 or 1066; those numbers are written as CCVII (two hundreds, a five and two ones) and MLXVI (a thousand, a fifty, a ten, a five and a one).
Symbols are placed from left to right in order of value, starting with the largest. However, in a few specific cases, to avoid four characters being repeated in succession (such as IIII or XXXX), subtractive notation is often used as follows:
I placed before V or X indicates one less, so four is IV (one less than five) and nine is IX (one less than ten)
X placed before L or C indicates ten less, so forty is XL (ten less than fifty) and ninety is XC (ten less than a hundred)
C placed before D or M indicates a hundred less, so four hundred is CD (a hundred less than five hundred) and nine hundred is CM (a hundred less than a thousand).

Arbeia was a large Roman fort in South Shields, Tyne & Wear, England, now ruined, and which has been partially reconstructed. It was first excavated in the 1870s and all modern buildings on the site were cleared in the 1970s. It is managed by Tyne and Wear Museums as Arbeia Roman Fort and Museum. This where I went to find some Roman Numerals, and came across this carving. It commemorates Regina, a British woman of the Catuvellauni tribe (approximately modern Hertfordshire). She was first the slave, then the freedwoman and wife of Barates, a merchant from Palmyra (now part of Syria) who, evidently missing her greatly, set up a gravestone after she died at the age of 30. (Barates himself is buried at the nearby fort of Coria (Corbridge).) The inscription reads as follows :-
D(IS) M(ANIBUS) REGINA LIBERATA ET CONIUGE
BARATES PALMYRENUS NATIONE
CATUALLAUNA AN (NORUM) XXX

Translating as

TO THE SPIRITS OF THE DEPARTED (AND) OF REGINA,
FREEDWOMAN AND WIFE OF BARATES OF PALMYRA,
CATUVELLAUNI BY BIRTH, DIED AGED 30