  Extensive air showers initiated by ultra-high energy cosmic rays are
sensitive to the details of hadronic interactions models, so we present the
main results obtained using the data of the Pierre Auger Observatory. The depth
at which the maximum of the electromagnetic development takes place is the most
sensitive parameter to infer the nature of the cosmic rays. However, the
hadronic models cannot describe consistently the maximum and the muon
measurements at energies higher than those reached at the LHC.
