In 1004 the Tuscolo hills welcomed a group of monks. An old holy man arriving, anxious to find a place to build a monastery to gather all his brothers. It was St. Nilus, born in Rossano, in Calabria, from a Greek family.

At that time Calabria was under the Byzantine rule and was Greek in language, culture, and spiritual and liturgical tradition. Nilus had founded several monasteries in Calabria and in Campania. Though a humble saint, he was held in high esteem by Princes, Emperors and Popes. Having flown from place to place to avoid all honours, he finally wanted to reach Rome to end his days in peace.

On the Tuscolo hills, the monks had been attracted by the wonderful ruins of a Roman villa, and by a low building in opus quadratum where there had been a sepulchre cell of the Republican era, and which had been adapted as a Christian oratory since the 5th century. Here St. Nilus and his followers stayed. Tradition says that in the Crypt, the Virgin Mother of God appeared to St. Nilus and to his disciple, the would-be St. Bartholomaeus, asking that they should build there in her honour a church, from where graces would flow on all neighbouring lands. Having obtained a gift of land from Count Gregorio of Tuscolo, the building of the Church and the Monastery began.

St. Nilus died shortly after. St. Bartholomaeus with other monks worked for 20 years building the Church, utilizing the material which had been abandoned in the Roman villa: pillars and pieces of marble, sculptured eaves and peperino blocks. In 1024 the church was completed, beautifully decorated with marble and paintings, enriched by sacred vestments and vessels admired by all. On December 17th of that same year Pope John XIX with a public ceremony consecrated the temple, dedicating it to the Mother of God, while the monks sang Greek hymns which St. Bartholomaeus himself had composed for the occasion.

Leaving the Church, one can see how all around it the monastery was built first in small dimensions, then it was enlarged more and more through the centuries with several outlying buildings. To the right of the Church there is a printing house; in front of it, the workshop used for restoration of old manuscripts and book. The monastery is also a center of culture, keeping in the "New Library" many old manuscripts left by St. Nilus and his monks.

In the XV Century the Abbey was envolved several times in the wars between Rome and Tuscolo. In 1241, for a period of 2 years, the Emperor Frederick II took possession of it, ruining it. Then came the mercenary troops (Ladislao of Naples, Nicolò Fortebraccio and Antonio da Pontedera XV Century). After all these troubles the Greek Abbey had a period of peace under the protection of the ‘Commendatario’ Cardinal Bessarione, first ‘commendatario’ abbot, a highly educated Greek scolar (1462).