Subiaco. In the middle of the 13th century the Emperor Frederick II made the abbey his headquarters during the siege of Rome, while in 1378 Breton and Gascon mercenaries held it for the antipope Clement VII. The fifteenth century saw the bloody feuds of the Colonna and the Orsini raging round the walls. According to the humanist Ambrogio Traversari, in 1432 the appearance of the abbey was that of a barracks rather than a monastery. In 1462 began a line of non-resident abbots in commendam, 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. Cardinal Bessarion, himself a Basilian monk, increased the scanty and impoverished community and restored the church. Cardinal Giulio della Rovere, for more selfish motives, erected the castle and surrounded the whole monastery with the imposing fortifications that still exist. Cardinal Alessandro Farnese replaced the ceiling. Gian Lorenzo Bernini was commissioned by Cardinal Francesco Barberini to provide the high altar, completed in 1665. Till 1608 the community was ruled by priors dependent on abbots in commendam, 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 commendatory abbots, and the first of a series of triennially appointed regular abbots was appointed. The triennial system survived the suppression of the commendam and lasted till the end of the nineteenth 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, but was restored by order of Leo XIII in 1881. 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. On 11 August 1901 the first electricity reached Grottaferrata from the hydroelectric plant in S. Bartholomew fall. On 26 September 1937, the monastery was made a territorial abbacy of the Italo-Albanian Catholic Church under the title Territorial