Michelangelo’s “Moses” was going to be a part of Pope Julius II’s tomb with more than 40 statues. Dream big, Julius: the final tomb was scaled way back, and only has 6 sculpted figures.
Moses was completed after Julius died. The horns may come from a mistranslation by Saint Jerome, meaning shining light. Basically the equivalent of a misused autocorrect. Way to go, Jerome.