In old school FORTRAN (I only recall WATFOR/F77, my uni's computers were quite ancient) subroutine (aka "subprogram") parameters are call-by-reference. If you passed a literal constant it would be treated as a variable in order to be aliased/passed by reference. Due to "constant pooling", modifications to a variable that aliased a constant could then propagate throughout the rest of the program where that constant[sic] was used.

"Passing constants to a subprogram" https://www.ibiblio.org/pub/languages/fortran/ch1-8.html

It's literally in the description? Because of aliasing, a variable that should've been zero became four.

It wasn't a variable.

It wasn't intended to be a variable, but it did become one. Its value varied, it's in the name.

But this is just Fortran's call-by-reference in action. It's not aliasing.