A Basilian monastery near Rome, sometimes said to occupy the site of Cicero's Tusculanum and situated on the lower slopes of the Alban hills, in the Diocese of Frascati, two and a half miles from the town itself. The monastery was founded in 1004 by St. Nilus, sometimes called "the Younger" or "of Rossano". This abbot, a Calabrian Greek, and hence a subject of the Byzantine Empire, had left Rossano in 980 to avoid the inroads of the Saracens and with his community had spent the intervening years in various monasteries without finding a permanent home. The legend narrates that, at the spot where the abbey now stands, Our Lady appeared and bade him found a church in her honour. From Gregory, the powerful Count of Tusculum, father of Popes Benedict VIII and John XIX, Nilus obtained the site, but died soon afterwards (26 Dec., 1005). The building was carried out by his successors, especially the fourth abbot, St. Bartholomew, who, is usually accounted the second founder. The abbey has had a troubled history. The high repute of the monks attracted many gifts; its possessions were numerous and widespread, and in 1131 King Roger of Sicily made the abbot Baron of Rossano with an extensive fief. Between the twelfth century and the fifteenth the monastery suffered much from the continual strife of warring factions: Romans and Tusculans, Guelphs and Ghibellines, pope and antipope, Colonna and Orsini. From 1163 till the destruction of Tusculum, in 1191, the greater part of the community sought refuge in a dependency of the Benedictine protocaenobium of Subiaco. In the middle of the thirteeth century the Emperor Frederick II made the abbey his headquarters during the siege of Rome, in 1378 Breton and Gascon mercenaries held it for the antipope Clement VII; and the fifteenth century saw the bloody feuds of the Colonnas and the Orsini raging round tile walls. Hence in 1432 the humanist Ambrogio Traversari tells us that it bore the appearance of a barrack rather than of a monastery. In 1462 began a line of commendatory abbots, fifteen in number, of whom all but one were cardinals.

The most distinguished were the Greek Bessarion, Giulio della Rovere (afterwards Julius II), and the last of the line, Cardinal Consalvi, secretary of state to Pius VII. Bessarion, himself a Basilian monk, increased the scanty and impoverished community and restored the church; Cardinal Giulio della Rovere, from more selfish motives, erected the Castello and surrounded the whole monastery with the imposing fortifications that still exist. Till 1608 the community was ruled by priors dependent on the commendatories, but in that year Grottaferrata became a member of the Basilian congregation founded by Gregory XIII, the revenues of the community were separated from those of the commendatories, and the first of a series of triennial regular abbots was appointed. The triennial system survived the suppression of the Commendam and lasted till the end of last century, with one break from 1834 to 1870, when priors were appointed by the Holy See. In 1901 new constitutions came into force and Arsenio Pellegrini was installed as the first perpetual regular abbot since 1462.

The Greek Rite which was brought to Grottaferrata by St. Nilus had lost its native character by the end of the twelfth century, and gradually became more and more latinized, but was restored by order of Leo XIII in 1881 (see Rocchi, "Badia", cap. iv). The Basilian abbey has always been a home of Greek learning, and Greek hymnography flourished there long after the art had died out within the Byzantine Empire. Monastic studies were revived under Cardinal Bessarion and again in 1608. The best known of modern Basilian writers is the late Abbot Cozza Luzi (d. 1905), the continuator of Cardinal Mai's "Nova Bibliotheca Patrum". Of the church consecrated by John XIX, in 1024, little can be seen except the mosaics in the narthex and over the triumphal arch, the medieval structures having been covered or destroyed during the "restorations" of various commendatory abbots. Domenichino's famous frescoes, due to Cardinal Odoardo Farnese, are still to be seen in the chapel of St. Nilus. In 1904 the ninth centenary of the foundation of the abbey was marked by a judicious but partial restoration, the discovery of some fragmentary thirteenth century frescoes and an exhibition of Byzantine art. The monastery has been exempt from episcopal jurisdiction since the days of Calixtus II, but its claims to the dignity of an abbey nullius were disallowed by Benedict. In 1874 the building was declared a national monument and in 1903 the church received the rank of a Roman basilica.

Raymund Webster.