In the early 6th century St. Benedict had founded 13 monasteries in the Subiaco area, residing himself as abbot of one of them: San Clemente. He was betrayed by the jealous priest Florentius who first attempted to poison St. Benedict and then tried to lead some faithful monks astray. It was at this point that St. Benedict, along with the first Benedictine oblates Maurus and Placid, and other dedicated monks, set off to find another place to call their sacred home.

Their divine path led them down the Liri Valley to the once noble and flourishing city of Cassino, arriving in the year 529 AD. After lent and on the arrival of Easter, St. Benedict destroyed the idols on the hilltop of Montecassino and converted the ancient pagan altar to Christianity, making it into a church dedicated to St. Martin of Tours. They also established an oratory to St. John the Baptist. This was the start of the construction of the abbey, which would eventually become one of the biggest and most influential monasteries in the world.

The first abbey of Montecassino was built by the monks themselves. They cut down the trees of the hilltop and gathered materials to build their new monastery together. They incorporated some of the ancient acropolis walls and tower into their structure and soon the people of Cassino began to assist in the effort as well in any way they could. St. Benedict oversaw the process, protecting them from the wicked presences he still detected on the once pagan site and even performing some miracles, such as saving the life of Severus, a monk who was crushed by a fallen wall.

The young abbey grew in both number of inhabitants as well as reputation. They received many visitors: guests such as Placid's father Tertullus, the poor and hungry from nearby towns, and novice monks. St. Benedict's devout sister St. Scholastica often visited with St. Benedict at a church nearby, Montecassino and the monastery in Piumarola where she was abbess. St. Benedict died in the mid 6th century at Montecassino, survived by his Rule, ideas, and devoted followers all over the globe. His earthly remains along with St. Scholastica's are located in a holy sepulcher inside the Cathedral of Montecassino.