For those who seek oddities in the center of Rome, the marble inscription on the side of the church of St. Salvatore alle Coppelle is a must-see. In Piazza delle Coppelle the inscription and box reveal the Church authorities’ concerns during the Jubilee of 1750.
The massive influx of pilgrims, who packed the city’s hotels and inns during this time, brought along concerns about the spread of epidemics across the Papal States. As a result, authorities constructed a number of spy post boxes around the city. The one in Piazza delle Coppelle may be the lone survivor.
About the source: Atlas Obscura
Atlas Obscura aims 'to inspire wonder and curiosity about the incredible world we all share'. You can contribute to their collection on their website.