The article presents first results of some acoustic measurement inside the Greek Theatre of Siracusa, and their comparison with computer simulations. The study shows the great acoustics of the Theatre and the consistency of simulated STI values with the measured ones. In addition, the comparison of simulated C50 shows an overestimation of the paramether, expecially at high frequencies. Moreover, on-field measurements showed some unexpected behaviour in two position, which will be investigated.