During field survey in the area of the Monti della Tolfa, carried out by the Gruppo Archeologico Romano between 1975 and 1984, a clandestine excavation was discovered. It yielded a concentration of pottery sherds from the rubbish dump of a small rural settlement of the second quarter of the second century BC. Some of the pottery was of local production, whilst some had been imported. The study of the finds in comparison with those from published sites dated to between the middle of the third and the end of the second centuries BC allows this pottery facies to be placed clearly within a quite precise chronological framework. This phase coincides with the construction, or the definitive laying out, of the Via Claudia, within the context of the general territorial restructuring that was taking place in South Etruria and central Italy, undertaken by the Roman state between the end of the Second Punic War and the middle of the second century.

The apse mosaic of San Teodoro presents numerous complicated problems. It has been heavily altered over the centuries, and the extent of these alterations has seriously impeded scholarly study. Comparison of the known extant antiquarian drawings, together with important unpublished archival documents, permits the reconstruction of its conservation history. This is considerably more complex than had been thought previously. The identification of at least four extensive, and often clumsy, restoration campaigns produces a new and precise definition of the parts of the original mosaic that survive. These manifest a level of quality scarcely imaginable earlier, and allow new technical and stylistic comparisons to be made in order to verify the commonly accepted chronology. The new documentation yields important information about the apse mosaic itself, and throws light on the history of Roman restoration workshops, mosaic-workers, materials and setting techniques.