It was the powerful Lombard family of the Castaldei who wanted it, together with many other fortresses in strategic places in the county of Capua. The Riardo Castle was built in the second half of the 9th century, on the hill overlooking the plain of the Savone stream, which arises from the extinct volcano of Roccamonfina.

From its position, on the slopes of the Trebulani mountains, the castle of Alvignano, the ancient Cubulteria, dominates the entire valley of the middle Volturno. The original structure, dating back to the 11th century, had probably incorporated a pre-existing square tower.

There is a castle inside the extinct volcano of Roccamonfina, on a natural saddle in the territory of the municipality of Conca della Campania. Its origin coincided with the birth of the fief of Conca in the12th century. The castrum, with a major tower in the south-eastern corner, was then reinforced with a belt of straight walls and watch towers.