San Marco has over 500 columns and as many capitals, unparalleled for their variety of types, beauty of workmanship, and rarity of material.
Along with a few classical capitals from the 3rd century, the most beautiful and numerous are the Byzantine capitals from the 6th to the 11th centuries. Some repeat classical forms, but most are among the most interesting products of Byzantine and Ravenna art.

Most of the material is scavenged from Constantinople, imitations, or replicas from the Middle Ages. Columns and capitals are arranged within the basilica, preferably following a rigorous symmetry of materials and shapes.
The spolia undoubtedly needed retouching or adaptation for their arrangement, while most of the bases of the Markan columns were made from scratch for their construction. The shaft and capital of a single column may have been created at different times and places, and even originate from different contexts. By combining them to form a new column, something entirely new is created.

The essential features relating to the arrangement of the columns in the interior of San Marco, predominantly from the 11th and 12th centuries, consist of a rigorous symmetry and correspondence, when the number of similar pieces allows it.
These features are dominant in the west arm where the marble shafts are distributed symmetrically, according to the grain, in a vertical or horizontal direction.
The distribution of the capitals in the presbytery area of the church is also regular and symmetrical, while for the columns it was necessary, perhaps due to the considerable size required, to arrange shafts of Proconnesian marble of different grains facing each other, and then a shaft of Dokimeion marble (light pavonazzetto) facing one of Proconnesian marble.

In the choir, in front of the pillars, two different pairs of capitals have been placed in a frontal position, so that the symmetry to the left and right of the axis is evident and a particular accent is placed in the apse, where the capitals with the richest decoration are located, the only ones present in the 11th century church.

These capitals, along with those in the lateral apses, immediately appear to be the most significant, and among them, four are placed on columns of green Thessalian marble, primarily because of their typology, which is the same as the main capitals in the church of Hagia Sophia in Constantinople. The capitals in the southern lateral apse are also Constantinopolitan works from the 11th century, while those in the main and north lateral apses are medieval copies of the same type. Therefore, only two spolia capitals were extant, and copies of the other six had to be made to have identical columns in all three apses. It is conceivable that the two spolia capitals were purchased in Constantinople with the intention of placing them in Venice, in a prime spot in the basilica. Perhaps the intention was to have capitals in Venice that were similar in decoration to those in the main church in Constantinople. At that time, it was likely impossible to find any other examples in Constantinople other than those two, and therefore, copies were necessary. The volute capitals of the apse and the Ionic ones on the walls of the west wing have their prototypes in the Justinian church of Hagia Sophia.
Regularity, alternating elements, and symmetry also prevail in the north and west narthex. In the north narthex, the interior walls were only fitted with Proconnesian shafts with equal vertical grain; as for the Ionic impost capitals, a single 6th-century capital is placed between each pair of medieval capitals. In the west narthex, the church’s main narthex, 6th-century Ionic impost capitals have been paired, even more than once, and placed in close proximity to pairs of 12th-century Ionic impost capitals, always on similar shafts of Proconnesian marble. In the west narthex, the side doors with pavonazzetto columns are flanked by particularly valuable impost capitals, featuring lion and eagle heads on facing globes, set on Late Antique shafts of black and white breccia, a marble originally from Aquitaine but, as documented, used in Constantinople in the imperial sphere as a particularly precious stone. Columns with rippled capitals were also placed in the splays of the side portals. These free-standing columns, which do not support vaults or anything else, were erected later, specifically during the façade’s decoration phase in the 13th century. These valuable columns, parts of which may have come from the area of the imperial palace in Constantinople, serve to thicken the row of columns on the west narthex wall, analogous to the dense sequence of columns on the west façade, and simultaneously enhance the façade’s appearance. Without these columns, the wall surfaces between the pairs of columns would have appeared bare compared to the façade. The contrast with the completely column-free west wall of the narthex is thus further emphasized: this contrast evidently stems from the intention to emphasize the interior wall of the basilica, which is the first thing one sees when entering, accentuated by the addition of further columns in the 13th century. Entering the narthex, a scene of great monumentality unfolds, based on the effect created by the free-standing, non-load-bearing black and white breccia columns, featuring fine capitals.