The twelve faces
In a previous outline it's been pointed out that there are cases where the image of the divinity was represented as a character with two or more heads; a sample of this can be found in the iconography of the roman god Janus and in its Christian developments.
The three faces of the divinity
Of course there is a great variety of iconographical expressions where this kind of symbolism was used.
Referring again to the sample of Janus,we know that his simulacrum could have two or four faces: (Macrobius – Saturnalia I, 9, 8 , also Servius, St. Augustinus ,etc)
in the first case the significance was related to the passage between what happened and what will happen;
in the second case, the four faces alluded to the "passages" of the four seasons; for this reason the meaning was more tightly connected with the cosmic symbolism of the annual cycle.
As far as the photo above is concerned, it shows a Christian sample of the divinity that is represented with twelve faces– Farneta Abbey (Arezzo-Tuscany); capital, rest of the ancient cloister-.
Trying to apply the quoted - above symbolism of the "heads", it seems possible to say that, in this case, the group of faces forms nothing but a cosmology, with reference to the annual cycle.
Therefore, the twelve faces altogether would represent the twelve months of the year (or, more likely, the twelve signs of the Zodiac).
It's possible to notice that, four of the twelve "heads" are bigger than the others; moreover they are bearded "heads" (with beards of different length) and are probably connected with the passages of the seasons.
We can add that, when the cloister still existed, the capital certainly supported one of the corners of the building, and it was probably the only capital decorated by sculptures.
Actually, the same meaning of the group of sculpted heads could give the idea of the whole thematic of the cyclic "time" as "cosmical year"; for this reason the inclusive iconography of the building needn't other symbolic underlinings .
All this was related with the need of every sacred place to symbolise, synthetically , the idea of an "universal" dimension.
About the reasons of the presence of symbolical meanings in ancient artworks.
or (Italian)
Il simbolismo cosmico nel tempio -cristiano-.
We are speaking of the need to express, in symbolic terms, the representation of a place "inhabited" by the divinity who, for his being "divine", cannot be limited by the dimensions of time and space.
It goes without saying that the cloister was a consacrated place.
Dealing with the Christian references of this kind of iconography, we notice the Sacred Writings pointing out the Saviour as he who will bring the "year of the Grace" Isaia LXI, 2 (II, 22, 1).
We can also remind of authors like Hippolitus of Rome: "As Day, Sun and Year were Christ, we have to consider Apostles as Hours and Months" (Be., Moses ; P.O., XXCII, 171) and Zeno of Verona who identifies the twelve Apostles in the twelve sunbeams that are the twelve months"(Tract. II,9,2).
Back to the Farneta Abbey, it can be remarked that you find the same iconography in the arch of a door that probably once brought to the cloister.
Iconografia medievale - Medieval iconography