At Roncobello in the Brembana valley, at 805 m a.s.l., east of the contrada of Forcella and north of the contrada dello Zucchero stand the remains of a castle datable to between the 12th and 14th century circa. The castle belonged to the Fondra family of Bordogna, which was granted the fiefdom of the area by the bishop from 1148 onwards, and for centuries was the most conspicuous of that region. Between the 14th and 15th century the family was active in the conflict between the Guelphs and Ghibillenes, in particular in the person of Lorenzo known as Triacha, one of the main Guelph faction leaders in the territory of Bergamo. He owned the castle and the tower in the locality of the same name.

It may be hypothesised that the structures were demilitarised during the 15th century, perhaps in the Venetian period. This seems to have been followed by the abandonment and destruction of the buildings and the robbing of the stone.

At the foot of the mount, on a small hill overlooking the valley, the investigation concentrated on the southern part where the entire area (80 m2) was excavated down to natural. This revealed the remains of a series of rooms with stone and mortar walls. The floors were of well smoothed strong greyish mortar. A large rock-cut cistern, accessed via a vertical well also seems to belong to this phase.

Further investigations in the northern zone identified other walls of the same date; what appeared to be an access via a downward slope to a gate or postern originally present on the west side and subsequently obliterated by the defensive walls of the subsequent period. At present it is not possible to define the precise characteristics and nature of this earlier complex. It may be suggested that it was a defensive structure built to watch over the valley in the medieval period.

Subsequently the fort was demolished and replaced by a new fortified construction surrounded by a pentagonal curtain wall which tapered towards the north and enclosed an oval space (circa 650 m2), divided in two by a wall. The curtain wall (4-5 m wide) was faced in split stones without the use of or with very little mortar, the internal cavity was filled with earth. The main entrance was in the south-east corner and was characterised by a long narrow passageway flanked to the east by a tower with sides of circa 7 m which formed the south-eastern corner of the curtain wall.

There was a similar tower in the north-western area, which skirted a smaller gate which constituted a link to the northern part of the complex.

A later phase attested by a wall in split stone and mortar with a plaster facing which completely surrounded the base of the hill. In the north-eastern corner was a gate which led to a track flanked by narrow stone walls.

The entire complex seemed to be a lookout pot and control point for the pass and the valleys below rather than an actual fortress.