In todays modern notation of Roman numerals 1954 is MCMLIV but the ancient Romans would have expressed them quite differently
1954 = MCMLIV
The Roman numerals are XLV.
18 in roman numerals looks like XVIII
20 in Roman numerals is XX.
300 would be represented by 'CCC' in roman numerals.
MCMLXXXIX
DCLXVI
MCMLII
XXI
XL
MCMLXV
MMI