The Roman, or Latin, system of writing numbers is still to be seen in academic circles.
It is mostly used to give copyright information; to carve dates in stone monuments; and to number such things as kings and the sub-divisions of plays. (Conventionally, the acts of plays (the larger divisions) are counted in upper case Roman letters - I, II, II etc - and the scenes (the smaller sub-divisions) in lower case Roman - i, ii, iii etc.) It is quite commonly used, in lower case, to number the prefatory parts of books - the Introduction, Contents page, Dedication, Acknowledgements etc before the 'real' book starts. Outside these, and various other hierarchical systems of numbering, AWE would not advise a modern writer to use it. It is clumsy, and difficult. But all students should be able to read it.
Here is a list of the first twenty numbers. This is enough to cover most of the 'numbering- applications - most plays have five acts, or fewer; and few acts have as many as fifteen scenes. And although you may come across Louis XVIII (the eighteenth) in French history, most names were less used than his. There have been a Henry VIII (the eighth) in England, and a James VII (the seventh) in Scotland; but twenty numbers is enough to cover the monarchs of most names in most countries. It is also enough for most prefaces in books, etc.
1 I 11 XI 2 II 12 XII 3 III 13 XIII 4 IV 14 XIV 6 V 15 XV 6 VI 16 XVI 7 VII 17 XVII 8 VIII 18 XVIII 9 IX 19 XIX 10 X 20 XX
To understand the system, and to be able to count beyond twenty, see Roman dates.