looks at watch
Well, damn, it's IIII. However my watch does use IX over VIIII, what's up with that?
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)
The reason I always heard is about ease of casting: it requires a more complex mold if 4 is written as IV instead of IIII.