In February and early March 2005, a geophysical survey was undertaken at Ostia Antica by the University of Southampton and the British School at Rome, on behalf of the Soprintendenza Archeologia di Ostia. The geophysical survey was successful in locating a substantial number of features in three areas at Ostia. It confirmed the presence of structures below the gardens of the Case degli Affreschi, below the Palestra at the Baths of the Forum, and in the vicinity of the river Tiber. The results also suggest the presence of earlier phases of settlement and buildings at Ostia, especially in the gardens of the Case degli Affreschi, and under the mosaic floor of the palestra. The limitation of geophysical survey techniques in such constrained areas was also noted, especially where understanding the phasing of structures is concerned.