The three trenches excavated in the House of the Mosaic Atrium (impluvium, garden, south-west corner of the southern ambulatory of the crypto-porticus) were undertaken as part of the Herculaneum Conservation Project. These excavations were among the scientific projects which provide data as back up to the conservation programme which is directed by the Archaeological Superintendency of Pompeii. Despite their limited size the excavations provided data of great interest regarding the building history of this residential complex. In particular, the work undertaken on the impluvium revealed that during the 2nd century B.C. phase, in correspondence to the northernmost lot (the existing atrium area) there must have been a garden or uncultivated open space, which may have been part of a dwelling that was laid out on a different plan and pre-dated the creation of the House of the Mosaic Atrium. The excavation in the garden also demonstrated that in the same period the adjacent lot to the south was an open space with traces of rich vegetation. Towards the end of the 2nd century B.C. a terracing or containing wall was built on this lot which perhaps corresponded to a property boundary towards the edge of the plateau. It was only in the Augustan period, on the northernmost lot, that the house with an impluvium in the atrium was built. Evidence was provided by an impluvium pool in opus signinum, with a drain, which was later re-lined with limestone slabs and finally with marble. The demolition of the terrace wall in the garden and a dump of earth rich in pottery fragments are contemporary with the construction of the impluvium which would suggest the contextual creation of the garden and peristyle. (Maria Paola Guidobaldi)