_______________________________ 1. ENEA Rome, 2. INGV Rome. 3. L’Aquila University. 4. University “la Sapien- za” Roma, Italy. 5. Soprintendenza speciale per i Beni Archeologici di Roma. 6. Istituto Archeologico Germanico, Roma, Italy. 7. S.D.R. Tokyo. 83 The importance of defining the geometry of foundations and soil layers for dynamic analysis of Colosseum Heinz-Jürgen Beste 6 , Paolo Clemente 1 , Cinzia Conti 5 , Gino D’Ovidio 3 , Giangiacomo Martines 5 , Yutaka Nakamura 7 , Luciana Orlando 4 , Rossella Rea 5 , Antonio Rovelli 2 Gianfranco Valente 3 Abstract By the comparison between tests and analyses, the dynamic charac- terization was performed, in order to obtain the map of elasticity mod- ules for soil Colosseum interaction. The accuracy for foundations and soil is lower than for monument, due to unknown exact geometry un- derground. For foundations, a high variability was found of elasticity modules, which was referred to variable damage of concrete for crack- ing in time. For soil layers, different definitions exist, and we are in- terested in the best. The vibrations produced by trains are depending on the underground geometry too. The analyses are performed with traditional convoys running on Metro B and C, for the vibrations knowledge on RA XLVII and on ground felt by pedestrians.