Geophysical investigations of the Olonium Roman site (Northern Como Lake)

The study area is located at S. Agata (Gera Lario), a small center at the n orthern end of Come Lake, near the junction of Valchiavenna and Valtellina Valleys. This site played a strategic role since ancient times, providing t he control on the communications routes to both the Come Lake and the Splug a and Septimer alpine passes. Since the end of the last century archaeologi cal findings are reported in literature, also supported, from the early XI century, by archival documents confirming the existence of the 'Olonium' se ttlement, an administrative and fiscal center of primary importance, as wel l as a parish amongst the most influential in the Como Lake area. Within an area of 45,000 m(2) an electrical survey has been carried out in conjuncti on with magnetic and GPR investigations. These studies have indicated the p resence of a number of sub-areas characterized by significant anomalies def ined by the overlapping of the results obtained from two or more geophysica l methods. In two of such sub-areas, excavation tests have been conducted, which have brought to light a number of archaeological findings of interest . In one of the two sub-areas, which is characterized by the superimpositio n of electrical and radar anomalies, a deposit of large pebbles has been fo und. The origin of this deposit has not been ascertained, whether it is of fluvial origin, related to the deviation of the Adda river in the Plan di S pagna region in Roman times, or it is part of reclamation works, still of R oman times, of paleolacustrine marshes. The overlapping stratigraphy, howev er, suggests the development of fluvial channels between Roman and Low-Medi eval times. In the other sub-area, excavations were carried out on sites de fined by electrical and radar anomalies, and confirmed by the results from magnetic survey. The excavations brought to light, below the fluvial deposi ts, a large medieval edifice, which could be identified as the S. Stefano c hurch abandoned in 1444. The church is built on earlier structures, amongst which an apse with a single aisle has been interpreted as a paleochristian sacellum. (C) 1999 Elsevier Science B.V. All rights reserved.