The Manhattan Project initially planned to build the pile at Argonne, far from Chicago, but Fermi then convinced Compton to assemble it beneath the West Curve of Stagg Stadium at the University of Chicago. Construction of the pile began immediately, under the direction of Zinn and Anderson and the supervision of Fermi. It consisted of a pile of graphite, uranium, and cadmium-coated wooden rods shaped like a rotational ellipsoid with a polar radius of 309 cm and an equatorial radius of 388 cm. Most of the uranium (6 tons) was at the center; the whole thing was supported by a wooden structure. The cadmium-coated wooden rods could be inserted at will and acted as reaction moderators, since cadmium is a strong neutron absorber.
