There's a theory[0][1] that it's mostly down to aesthetics. It looks visually more pleasing that way when split into three groups of four numbers: I, II, II

There's a theory[0][1] that it's mostly down to aesthetics. It looks visually more pleasing that way when split into three groups of four numbers: I, II, III, IIII (consisting of I only) V, VI, VII, VIII (consisting of I and V) IX, X, XI, XII (consisting of I and X) [0] http://mathtourist.blogspot.co.uk/2010/08/iiii-versus-iv-on-clocks.html http://mathtourist.blogspot.co.uk/2010/08/iiii-versus-iv-on-... [1] https://www.hautehorlogerie.org/en/encyclopaedia/glossary-of-watchmaking/s/roman-numeral-iiii-on-dials-1/ https://www.hautehorlogerie.org/en/encyclopaedia/glossary-of...