Sandi Toksvig made the point in a QI episode that if you use IIII, you get a pleasing symmetry with the number of Vs and Xs on a clock face. Four numbers with o

Sandi Toksvig made the point in a QI episode that if you use IIII, you get a pleasing symmetry with the number of Vs and Xs on a clock face. Four numbers with only Is, four numbers with a V and four numbers with a X. I'd be surprised if that was the reason, but it's kind of neat. I II III IIII V VI VII VIII IX X XI XII