Preposition for "working at a university"

Question

Usually we use the preposition bei to describe working at a company:

Ich arbeite bei der Firma Siemens.

and the preposition an for studying at a university:

Ich studiere an der RWTH Aachen.

What about working at a university? Should it be an or bei or others?

Ich arbeite (als Professor/Dozentin/Hausmeister) _____ der Uni Heidelberg.

Answer 1

Only "an der" is correct unless you're not teaching at this university, then you would work "für die"university. If you would say, I work "bei der" university, then you'd only work nearby."In der" would be correct but it's pretty outdated to say.

Answer 2

All of an der, bei der, in der and für die are acceptable with arbeiten. One might tend to prefer an for professors.

(Just as Crissov said in the comments)