The Cosmatesque Cloister, so beautiful with its symmetrical little pillars, columns and capitals is a real gem of Romanesque-Cosmatesque architecture. On the West side of this cloister there is an ambulatory with a vault and a series of arches in perspective covered with frescoes (XIIIth-XIVth centuries).
Of particular interest are the paintings on the wall (XIVth century) depicting churches and fortresses of territories belonging to the Abbey. Above the central arch on the Southern side is the inscription: Magister Jacobus Romanus fecit hoc opus. On the West side is another inscription: "Cosmas et filii Lucas et Jacobus alter Romani cives in marmoris arte periti hoc opus expleverunt abbatis tempore Landi".
Therefore the cloister was built in two stages. The South in lime stone was built with great exactitude towards the end of the XIIth century or in the early years of the XIIIth century by James, son of Lawrence. The other sides were constructed during the regime of abbot Lando (1219-'43) by Cosma, son of James and by Cosma's sons: Luke and James II. For these three sides was used white Carrara marble taken from the ruins of St.Benedict's first monastery which was destroyed by an earthquake.
On the South side built by James, "everything is simple and pure but very impressive; the vigorous contrast of light and shade of Roman architecture which we notice here reminds us of the sides of the temple of Malatesta at Rimini" (Lavagnino). This side was probably built at Rome and afterwards mounted here; in fact the stones are all numbered or marked in various ways.
Northern side
The northern passageway of the Cosmatan Cloister parallels the church: it is the long side of an asymmetrical rectangular with an opening which is not in the middle but in the west, and which is characterized by a curved, round, flattened arch which is founded, on each side, on the one massive capital of two columns placed on the little wall which separates the passageway from the rest of the cloister. Looking at the opening from the well, on the left you see a double lancet window, whose small, round, curved arches are founded, in the middle, on the capital of two interwoven columns with one base, while on the two sides there is a sturdy pillar placed on the little wall. On the right of the opening there is a double lancet window, which is identical to the one on the left and, next to it, a couple of five small, curved arches, founded on the capitals of different columns: coupled, polished and twisted columns which alternate: the first and the last small arches are founded on pillars which are identical to those previously described. Even though unsystematic, the northern side of the Cosmatan cloister is harmonious, on the whole; it is in line with its middle-age architecture.
Eastern side
The eastern passageway of the Cosmatan Cloister is the shorter side of the cloister itself which has got an asymmetrical rectangular shape. The opening is in the middle and has got a round, curved arch. It is slightly bigger than the other arches, it is founded on the capitals of two coupled columns and, on each side, has got a four-lancet window, whose small curved arches are founded o the squat capital of a sturdy pillar. Looking at the opening from the well, you see, next to the pillar, a double lancet window, which is mad up of an alternation of single, polished columns and coupled polished ones, whose round arches are big and airy. Instead, the left four-lancet window, though having columns with similar features, has got much smaller and more narrow arches. However, thesedifferences don't obstruct the beauty of the Cosmatan cloister.
Southern side
The southern passageway of the Cosmatan Cloister is the long side of the asymmetrical rectangular plant of the cloister itself. The opening, corresponding to that of the northern side, is characterized by an arch founded on the capitals of two sturdy pillars, placed on the inner little wall. The round arch is higher than the other ones and has got a centring which touches the projection of the cornice, on which there is the front of the monastery. Looking at the opening from the well, on the right of the pillar, you see six narrow, curved, round arches founded on the big capitals of polished columns, which alternate: the first column next to he pillar is single, the next is coupled and so on. On the left pillar a overturned human head is drawn with red paint. Next to it there are six small, curved, round arches founded on single, polished columns alternating to coupled ones. The last arch is founded on a big pillar, next to which there are other six small aches founded on other alternating columns. The piece of the arches are progressively numbered from I to XVII and on each pillar there is the same sign which is on the nearby horizontal slab: most probably the work was done in Rome and then brought here and reassembled.
Western side
The western passageway of the Cosmatan Cloister is slightly longer of the Eastern one. There is no opening on the inner wall, but there are columns and small arches that give real, undeniable and harmonious elegance to the wall cloister. Having your back to the octagonal well and looking at the western side, on the right you see a four-lancet window, whose middle column are coupled and polished, while the side columns are single and polished; the curved, round small arches are founded on a corner pillar and, on the left, on another pillar. In the middle of the small wall, where the opening should have been, there is a middle, round, curved arch, which is founded, on each side, on two polished columns, flanked by a four-lancet window: that on the right has got two interwoven columns with the same base, while that on the left is a spiral column. On the left of the pillar, there are other small arches, but they are bigger, round, curved and founded on polished columns, a part from the middle one which is couple