I have seen a number of posts requesting information about Gospel Harmonies. I just stumbled upon this classic harmony included within my LOGOS library, THE DIATESSARON OF TATIAN:
logosres:anf10;ref=Page.p_33
From the information that I have, it is one of the (if not, the) earliest known attempts at harmonizing the gospel stories into a single story. I am posting this note so that others looking for help with the harmonies might see it when searching the forums. Perhaps MJ or others know more of its history than I do.