The church of San Calocero in castro stood on the hill of Caluso, south of the castle's walled circuit, and its existence is dated back to 1177. What remains today are ruins, but they are enough to recognise its Romanesque origin: the base of the masonry says so, and so does the canonical orientation towards the east, where the building must have continued and closed with the apse.
What to see
It is worth looking closely at the walls, because a number of Roman lateres are embedded in the fabric, the flat bricks of the imperial age: whoever built the church took material where it lay, and at Caluso what lay to hand was the legacy of the Roman oppidum. With a little attention you can make out, inside the south side, a rectangular niche, perhaps meant for lamps, and on the northern side, the one facing the castle, a door later blocked up: there is no telling whether it was the main entrance or a secondary one. The rest is a roofless shell of walls in the long grass, with two corner piers still standing.
Visiting
The importance of this church lies in one word: castrense. It was not the village parish but the church of the fortified system, under the protection of the castellans. And the castellans, from the early Middle Ages on, wanted warrior saints as patrons: the Saint Michael brought by the Lombards, whose patronage runs through the whole Middle Ages in the Canavese, at Candia, at Rivarolo, at Brosso, at Strambino. In that logic it is no surprise that Caluso settled on Calocerus, a martyr of the official calendar: a man who had defended his own faith with valour would do as much for his devotees.
Our editors' tip
Do not come here expecting a church: what you see is a ruin, and it has to be read the way you read a ground plan. Find the east-west axis first, then picture the apse where the walls break off, and at that point the blocked door on the north side takes on meaning: it faced the castle, that is, the people who came into this church first. Make the visit together with the Castellazzo, which stands on the same hill a few dozen metres higher; and the right season is late summer, when the grass is high and the red bricks are the only thing that stands out against the green.