Monte Mario Observatory
Rome, Italy
The Monte Mario Observatory (Sede di Monte Mario, literally "Site of Monte Mario") is an astronomical observatory and is administratively part of the Observatory of Rome (Osservatorio Astronomico di Roma). It is located atop Monte Mario, near the right bank of the river Tiber, in the municipality of Rome, Italy. This location (12°27'8.4"E) was used as the prime meridian (rather than that of Greenwich) for maps of Italy until the 1960s.
Observatory data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).