On the Castelmur promontory there are ruins of a massive early medieval fortified wall with a gateway in the center, where tolls were once collected. This wall is called Lan Muraia.
Built on a rocky terrace overlooking the Maira River, Lan Müraia was constructed to protect the old road. It also marked the political border between the territories of Sottoporta (below the gateway) and Sopraporta (above the gateway), or, more precisely, the holdings of the bishops of Como and Chur.
The name "Porta" describes the geographical bottleneck of this area and comes from the name "Porta Bergalliae," already mentioned, along with the castle, in the imperial Rhaetian archives of 841 AD.
In 250 AD, the wall was referred to by the Romans as the milestone of Murus. Archaeological excavations have revealed a settlement dating back to the Roman Empire. There are traces of different buildings, including one with a hypocaust (an ancient Roman underfloor heating system) and two alters out of soapstone.
Nossa Donna and Castelmur fortification
Heading from Stampa toward the Italian border, just before Promontogno, on top of a promontory that divides the valley, stands the church of Santa Maria di Castromuro, better known as Nossa Donna, and an imposing five-story, square tower. This tower dates back to the 14th century and is all that remains of the feudal castle Castelmur. The castle was built about a century before the tower and little was preserved.
The name of the castle is named after the influential Bregaglian Castlemur family, who, at one time, lived in the castle. In the 15th century, the fortress, which was also part of Lan Müraia, lost its military importance and fell into disuse. Soon after, it turned into ruins. In the Middle Ages, Bregaglia formed a single parish under the the Diocese of Chur, and Nossa Donna was the valley's main church.
After the Reformation, the church lost its importance and, in the 16th century, fell into disrepair.
During the years 1845-50, Baron Giovanni Castelmur of Coltura had the church rebuilt on its old foundation up to the Romanesque bell tower. The tomb of Baron Castelmur and his wife is in the crypt of the church.