TITLE: Did Grothendieck write about modular forms?
QUESTION [16 upvotes]: This question might be astoundingly naive, because my understanding of modular forms is so meek. It occurred to me that the reason I was never able to penetrate into the field of modular forms, automorphic forms, the Langland's program and so forth was because my appeal is to things that have the feel of SGA1, and those things do not.
I was wondering, therefore, if Grothendieck had devoted thought to this, and if so where it can be found, and how it is treated in the field at the moment.

REPLY [4 votes]: Grothendieck was aware (at least) of modular forms and their relations to motives by J P Serre in a letter dated December 31, 1986.

Grothendieck (also) develop on "La longue Marche" a theory of "topos modulaire" (now completely available online!).