The remains of the ancient tower that stands on the top of Colle San Geminiano, is what still exists today of the ancient Castle (or "Castrum") of the Ghisalbertini De Martinengo Counts, who bought it in 1045, becoming the lords of Mezzate ( today Bagnatica).
Originally the tower was inserted in a much more complex fortified structure, surrounded by defensive walls, inside which other buildings were built, including the church dedicated to San Geminiano (no longer existing) and a well, whose remains are still visible.
This castle, like many other fortifications in the area, had a defensive function of the plain, thanks to the excellent view from the top of the hill.
The De Martinengo counts enjoyed a position of power for a long time from the time of the purchase of the Castrum, but the fights between families that took place in the 13th century caused them to fall into ruin, losing all power over the territory.