The castle site has been occupied and fortified since at least the Roman era. The important trade road over the Septimer Pass runs through the Val Bregaglia. At Bondo the valley narrows leaving a narrow passage between the Maira river and a large rocky outcropping, making the castle site an ideal location for a customs station and fortification. The Romans built a guard station and village named Murus according to the 3rd century Itinerarium Antonini. The foundations of several buildings as well as one building's hypocaust and two small votive altars have been excavated from the Roman settlement.