The south-west side of the municipality, where the Abbey of Campoleone originated, is perhaps the richest in memories and historical events. Here Romans and Longobards, more than elsewhere, settled on the hills; here arose the ancient Parish Church of S. Giovanni and Sietina. The closest castle to Campoleone today is called Castelluccio. Perched on a hill, opposite the famous abbey, and separated from it by a stream, it rose on the northern edge of the swamp. Among its ruins, referable to sec XI and XII, you can see on the east side the door jambs of a portal and a short stretch of wall known as 'la portaccia,' while on the western side, there is a group of medieval buildings that form the village.

According to tradition, the name Castelluccio comes from Lucio Metello, a consul who was once the governor of Arezzo. The same tradition says that Campoluci, a village opposite to Castelluccio, corresponds to Campo di Lucio, where the consul died.

The castle's church is dedicated to St. Michael the Archangel and is located at the top of the castle. In the 14th century, it was known as Sant'Angelo in Fabriciano and was united with the church of Santa Maria Maddalena in Sietina in 1770. The church was completely rebuilt in the second half of the 19th century. On the right side stands the bell tower with the clock that replaces an older bell tower. The interior has a nave, rataining a wooden group depicting the Madonna and Child, which was heavily repainted and may have come from the nearby Abbey of Capolona. The sculpture is surrounded by 15 painted panels depicting the Mysteries of the Rosary, from the Vasari school of the second half of the 16th century.