This overlaps slightly with this question; That question is more general about statues and can naturally be applied more generally to other historical depictions of important figures. In this question I want to ask specifically about the Alexander Mosaic.
I have been unable to find any reason why we are so confident that the Alexander Mosaic in Pompeii actually depicts Alexander the Great and not some other general/ruler.
Not only do every source I find claim to know who it is, but also which battle it depicts, despite Alexander the Great and Darius III having clashed more than once.. That seems even more farfetched.
How do we know so much about this mosaic?