The has several courts, which lead to the famous
portico designed by
Antonio da Sangallo the Younger, with an arcade of nine bays supported by slender columns with Renaissance capitals. Of the abbey church consecrated by John XIX in 1024, little can be seen in the interior except the mosaics in the
narthex and over the triumphal arch, the medieval structures having been covered or destroyed during the "restorations" of various
abbots in commendam. Some fragmentary thirteenth-century frescoes were revealed in a partial restoration of the church in 1904 to commemorate its novecentennial, when it was made a Roman
basilica. The mosaics portray the
Twelve Apostles sitting beside an empty throne, evoking Christ's ascent to Heaven.
Domenichino's frescoes, commissioned by
Cardinal Odoardo Farnese in 1608, can be seen in the chapel of St. Nilus.
Annibale Carracci executed the altarpiece of the
Madonna with Child with St. Nilus and St. Bartholomew. The modern portico protects the ancient façade; the marble portal with a mosaic above it, an example of Italo-Byzantine art of the twelfth century. In the interior is a baptismal font supported on winged lions, of the tenth or eleventh centuries. Noteworthy also is the Romanesque
campanile (twelfth century), with five storeys of tripartite arched windows. The library of the Abbey, which contains some 50,000 volumes, has a paper conservation
Laboratorio di Restauro, which was entrusted with the conservation of
Leonardo's
Codex Atlanticus from the
Biblioteca Ambrosiana; the library houses writings of St. Nilus and his pupils and a rare copy of
Alvise Cadamosto's collected travel accounts, printed in the early sixteenth century. The monastery's library also includes the largest collection of
Greek-language manuscripts pre-dating the year 1600 found in a monastery anywhere in Western Europe. The founders of the monastery had come from
Calabria and brought with them the tradition of Greek-speaking settlements in Southern Italy and Sicily. Of the more than 200 Greek language manuscripts in the collection, forty of them consist of
music notation, most of which are written in the
Byzantine Rite that pre-dated the reforms made to
Byzantine music by
John Koukouzeles in the 14th century. The library has many rare manuscripts of Byzantine music, some of which contain types of music and notation that eventually fell out of favor in the East and were not well preserved in that region.
Pope Benedict IX died and was buried in this abbey. ==International relations==