Design and status of the Mu2e Calorimeter

The Mu2e calorimeter is composed by $\sim 1400$ un- doped CsI crystals coupled to large area UV extended Silicon Photomultipliers(SIPMs) arranged intwo annular disks. This calorimeter has to provide precise information on energy, timing and position resolution. It should also be fast enough towithstand the high rate background and it mustoperate and survive in a high radiation environment. All steps done for the construction and test of the Module -0 prototype, that is an array of51 pre-production crystals, are reported. The Module -0 was exposed to an electron beam in the energy range around 100 MeV at the BTF (Beam Test Facility) inFrascati. Preliminary results of timing and energy resolution at normal incidence are shown.