The conservation treatments carried out between June 1992 and August 1993 on the architectural remains of a Byzantine basilica in Petra, Jordan, during and immediately after the excavation are described. The treatments completed during excavation included: stabilization and consolidation of certain sections of the basilica's sandstone ashlar masonry; cleaning and consolidation of the unpainted lime wall plaster decorating the basilica interior; cleaning and consolidation in situ of the extensive remains of a figurative mosaic pavement in the two side aisles, and the fragmentary remains of the opus sectile pavement in the central aisle. The consolidation treatments included injection grouting using hydraulic mortar mizes produced in Italy, and mortar repairs using slaked lime and hydraulic lime. The existence of the mosaic required preventive conservation measures during the excavation, such as the construction of a temporary shelter over the site during the winter, the use of temporary protective facings over damaged areas of the mosaic, as well as the temporary backfilling of the mosaic with soil ofer a layer of geotextile in order to protect the mosaic between the initial phase of conservation work and the construction of a permanent shelter for the site in the near future. The importance of having a conservator present on site during the criticala phase of excavation, when all materials are most susceptible to damage, is emphasized. The Petra Church Project will hopefully serve as a model for future excavations in that it employed two conservators from the beginning of the excavation: one for small finds, the other responsible for the site and the architectural remains removed from the site during the excavation.