The Roman site of Miróbriga (Santiago do Cacém), located in modern Alentejo/Portugal, had developed from a Celtiberian oppidum and embraced public facilities such as baths and a forum (their construction began as early as the 1st century AD), as well as small commercial structures (tabernae) located mainly in the urban centre. The present investigations concentrate on private residential architecture (domus) discovered through geophysical surveys carried out during the last 8 years. The careful excavations of peristyle houses provide us for the first time with the possibility to reconstruct the architectu ral history of private buildings in the small urban centres of southern Lusitania, which shows several changes until the second half of the 3rd century AD(the so-called “crisis of the 3rd century”).