Enrico Fermi and his team from Columbia University arrived at the University of Chicago in January 1942 as part of an effort to concentrate the Manhattan Project's reactor work at the new Metallurgical Laboratory. Fermi arranged with Wigner for Christy to join his group, which was building a nuclear reactor, which Fermi called a "pile", in the squash court under Stagg Field at the University of Chicago. Construction began on November 6, 1942, and Christy was present when Chicago Pile-1 went critical on December 2.