Following the betrayal of an envious priest named Florentius, St. Benedict left Subiaco where he had established a community of monasteries, serving himself as one of the abbots. With his faithful disciples Placid, Maurus, three guiding ravens, and other devoted monks, St. Benedict followed a divinely inspired path. They arrived to Cassino, around the year 529 AD. They found Cassino in dire need of revival, inspiration, and faith, the people of Cassino having returned to a mixture of Christian and pagan worship after a long period of decline in their town. This, St. Benedict understood, would be the new project God had destined him to undertake.

On the pagan summit remained an ancient temple to Jupiter, an altar to Apollo, Roman guardian towers, pagan idols, a sacred grove, and a cyclopean wall. Having been granted the property from Placid's father Tertullus, a Roman patrician, they began construction on the hilltop above Cassino. St. Benedict confronted the pagan remains, destroying the idols and converting the Temple of Jupiter into a church dedicated to St. Martin of Tours, founder of monasticism in France in the 4th century. The church would have been modestly sized, around 7 X 7 meters and able to hold about 30 monks. Above the altar to Apollo they built an oratory dedicated to St. John the Baptist. The rectangular oratory had bigger dimensions at 7.6 x 15.25 meters, and would eventually become the resting place for St. Scholastica and St. Benedict. The subsequent churches as well as today's Cathedral of Montecassino were all to be built on the same site of this first humble oratory.

St. Benedict held hard work, including manual labor, in high regard. As such, the monks constructed these original structures of the primitive monastery themselves, using the trees and other materials from the sacred grove on the hill. St. Benedict preformed a number of other miracles during and after the construction of the first abbey of Montecassino, including what is considered his most important miracle: writing The Rule of St. Benedict. This was his sacred home until his death in the mid 6th century. He died in prayer, with two devoted monks by his side. A bronze statue commemorating this moment can be seen in the garden, on the spot where the primitive oratory once stood. The first destruction of Montecassino followed a few decades after St. Benedict's death, in 577 AD.