Aren't COMMON's implemented as static structures? Stuff that's accessible from multiple functions - except that Fortran requires explicit rather than implicit reference.

It is way of sharing variable values without using parameters. But it is ugly and easy to make errors, e.g. accidentally missing a variable out of the middle of the list in one function or subroutine means all the later variables have unexpected values.

It is a log time since I did any FORTRAN. Maybe they improved it?