In the days BW (Before Word), monks hand-lettered the italic fonts into blank spaces left on the typewritten page.
(Serious answer, people used the underscore _ to underline on typewriters. Underlining was thus typesetter's code for "italics"; and that's what was expected in manuscript format. Online, to simulate that, people often put "_"s in front and back, like _this is in italics._ Having done that since I was a wee lad, I find I _still_ do it; and it's still the syntax I recommend for use in the Critters workshop, where text is the least common denominator format.)