  CALIFA is the high efficiency and energy resolution calorimeter for the
R$^{3}$B experiment at FAIR, intended for detecting high energy charged
particles and $\gamma$-rays in inverse kinematics direct reactions. It
surrounds the reaction target in a segmented configuration of Barrel and
Forward End-Cap pieces. The CALIFA Barrel consists of 1952 detection units made
of CsI(Tl) long-shaped scintillator crystals, and it is being commissioned
during the Phase0 experiments at FAIR. The first setup for the CALIFA Barrel
commissioning is presented here. Results of detector performance with
$\gamma$-rays are obtained, and show that the system fulfills the design
requirements.
