I'm no scientician, so I'll quote the Manhattan Project entry from Wikimopedia:
The first major scientific hurdle of the project was solved on December 2, 1942, beneath the bleachers of Stagg Field at the University of Chicago, where a team led by Enrico Fermi, for whom Fermilab is named, initiated the first artificial self-sustaining nuclear chain reaction in an experimental nuclear reactor named Chicago Pile-1. Compton reported the success to Conant in Washington, DC by a coded call, saying, "The Italian navigator [referring to Fermi] has landed in the new world, the natives are friendly."There's supposed to be a marker around here somewhere making note of the event, but I haven't been able to find it yet.
One of our readers posted a response below letting us know where the marker is. Unfortunately, instead of being friendly and helpful he decided to be rude and insulting, so his comments have been deleted.
But the upshot is that there is a marker. It is on Ellis Avenue, south of East 56th Street. Sadly, such an important monument is not noted on the University of Chicago's campus maps.
The reader incorrectly claims that Stagg Field no longer exists, though it is clearly labeled on U of C's campus maps. As colleges are always evolving, it is likely that Stagg Field was once larger, or in a different location, or both. But it certainly exists.