The church of the Beata Vergine Assunta stands in the hamlet of Piaggio, on a spur of rock on the right bank of the Ovesca, and it has a form you will not find elsewhere: two churches one above the other, the paired apses of the upper resting on those of the lower. Its raised position and the word castello, which appears as a place-name in old documents, suggest that the primitive building was a castle chapel serving a fortification set to guard the via francisca, which climbed the valley and divided just there between the branch for the Antrona valley and the one for Domodossola.
What to see
The oldest chapel is the northern one, now below road level: it is reached through a door under the sacristy and along an underground corridor that crosses the whole church. It is dated to the eighth or ninth century, Carolingian or even Lombard, which places it among the oldest surviving sacred architecture in the Val d'Ossola. It is a single hall with a semicircular apse facing east, lit by two double-splayed single-light windows, with traces of frescoes. Later it was widened by cutting into the rock westwards, doubling its width and adding a second apse.
Visiting
In the eleventh century, perhaps after a flood of the Ovesca had buried the old church, a new one was built higher up, with two naves resting exactly above the old ones; to carry them the halls below were strengthened with a central pillar and cross vaults, as is done in crypts. And as a crypt the lower church went on serving, to judge by the surviving frescoes, at least until the fifteenth century. The walls of the new church are made of river cobbles and a great deal of mortar, a rough technique compared with that of San Bartolomeo close by. At the end of the sixteenth century two arches were opened in the south wall to link a smaller nave, and in 1878 the northern door became the main entrance.
Our editors' tip
The reason to come all this way is in the northern apse of the upper church. In the semi-dome is painted a Trinity at the altar: the three Persons shown as three identical images of Christ, seated frontally at a table, each holding the eucharistic chalice. It is one of the oldest known representations of this type, and it remains startling even to those who take no interest in iconography. Below, on the curved wall of the apse, are six apostles in pairs, separated by the windows; another six must have stood in the southern apse. The frescoes are dated between the end of the twelfth century and the thirteenth, but the style is the hieratic one of earlier Romanesque, which lasted a long time in the alpine valleys.