  Calorimeters with a high granularity are a fundamental requirement of the
Particle Flow paradigm. This paper focuses on the prototype of a hadron
calorimeter with analog readout, consisting of thirty-eight scintillator layers
alternating with steel absorber planes. The scintillator plates are finely
segmented into tiles individually read out via Silicon Photomultipliers. The
presented results are based on data collected with pion beams in the energy
range from 8GeV to 100GeV. The fine segmentation of the sensitive layers and
the high sampling frequency allow for an excellent reconstruction of the
spatial development of hadronic showers. A comparison between data and Monte
Carlo simulations is presented, concerning both the longitudinal and lateral
development of hadronic showers and the global response of the calorimeter. The
performance of several GEANT4 physics lists with respect to these observables
is evaluated.
