Il duomo di Monreale

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I Mosaici in opus sectile del Duomo di Monreale

The website is today the most comprehensive treatise of the geometric decoration of Monreale Cathedral. It was conceived as a collection and presentation of a part of our drawings and studies of the subject. Our intention is to give a complete digital representation of the floor and lower walls' geometric decoration in the Basilica. The reproduction is made by PowerCADD redrawing of each work. Therefore the pictures lack those inevitable irregularities and imperfections, which often make works' look more attractive than the perfectly made ones. The plans' orientations are usually the same as the Basilica: east up, west down.

The author was born 23-3-1949 in Termini Imerese [near Palermo] and teaches History of Art at the Secondary Classic School "Umberto I" in Palermo. The presented material is the result of studies carried out in the Cathedral during 15 years' activity at the Istituto Statale d'Arte del Mosaico in Monreale.

To the Ecclesiastic Authorithies of the Cathedral we pay our respects and due thanks.


All sections are still partly incomplete since the site is in progress. We apologize for this inconvenience and, unfortunately, we must postpone the presentation of a more satisfactory repertoire to future dates.

Monreale Cathedral, side portal exit, square typology. [Design by G. Oddo - Digital elaboration]

When we talk about “Monreale mosaics”, we must obviously refer to the whole body of pictorial works of figurative character [stories of the Old and New Testament], which covers almost all the high parts of the Basilica structures. Their theme has always aroused interest and enthusiasm in so many renowned scholars that we are by now in possession of a rich and impressive bibliography, the best of which are the works of Benedetto Gravina and Ernst Kitzinger, which can be considered the main undisputed authors.

However, within the sphere of the decorative works, there is a branch which has basically remained unexplored and towards which scholars –when interested-have paid only a brief attention, sometimes even haughtily, probably for their incapacity of finding (in a world made of strictly geometric shapes, governed by mathematic laws which regulate their constituent method) any aspect worth of treatment. It’s the branch of the decorative mosaic in opus sectile. Our studies and research deal with these types of works and aspire to fill this gap because this field deserves to be enhanced and analyzed deeply, just like the figurative one.


Palermo, Palatine Chapel, figurative motif b and m. The number of figurative models of the “Palatine” is extremely limited, compared to those ones of Monreale Cathedral. For this reason, and also to render an immediate idea to which of the two monuments one belongs, we decided to apply different methods of classification, using the alphabetical letters for the Palatine and numbers for Monreale Cathedral. [Designed by G. Oddo - Digital elaboration]

The material we are going to show in the site, in digital elaboration, is only a part of a much wider editorial project totally dedicated to the publication of the geometric motif of the mosaics in “opus sectile” of Monreale Cathedral.



On the left: Monreale Cathedral. In the middle:Palatine Chapel.On the right: Martorana church, Palermo. [Photos by B. Hoffmann]


On the left: “the panel represents a wonderful scene, where we can see some columns surmounted by a cupola and Saint Paul baptized by Saint Anania through the complete immersion in a pool inside the baptistery, according to the ancient method, but outside the temple. Saint Anania is represented with the right hand alighting on Saint Paul’s head, in the act of christening him, while a God’s launched ray, with the dove clear symbol of the Holy Ghost, hits Saint Paul’s ear. A man in a White tunic and with a candle in his hands is present at the ceremony”. [La Cappella di San Pietro nella reggia di Palermo, 1987 parte II, pag.9] On the right: “the panel represents St. Peter imprisoned, enchained and controlled by sleeping armed guards; an angel appears to the Saint and in the golden field of the picture we can read the inscription: "praecipit Angelus Petro ut cito surgat et velociter carcere exeat". [La Cappella di S. Pietro nella Reggia di Palermo, 1987, Palermo, Parte II, pag. 9]

On the left: “the picture shows an image of St. Egidio which is bigger than usual thanks to the mosaic’s tesserae; from his aspect we have the impression to look at a portrait.” On the right: “on the panel we can see St John Chrysostom reproduced in a bigger size than normal, with the mosaic’s tesserae underlining every facial muscle, every part of his head and his drape.” [La Cappella di S. Pietro nella Reggia di Palermo, 1987, Palermo, Parte II, pag. 9]. Palermo, Palatine Chapel. Details of St. Egidio’s and St. John Chriysostome’s images, placed on the piers of the arches of the Church. 5. The difference we can immediately catch from the comparison between the two executive techniques of opus tessellatum and opus sectile is that the first presents only square shape tesserae, the second instead, uses different but regular types of geometric motif.

Reproduction of the works in digital format

The peculiarity of this kind of work (of which we are presenting only a limited sampling of texts and images) consists in the digital reproduction of two types of decorative works of pictorial aspect concerning Monreale Cathedral: the pilasters and the floors. With the words “digital reproduction” we mean a computer-based procedure applicable only to the possibility of using a lot of single panels [or crustae] or joined panels [pieces] in order to succeed in composing the whole picture totally. Moreover there is also a laborious phase of studying and interpreting the proportional structure of the mosaic series, above all as regards the double codes figurative texts (a significant example of this genre is the graphic of the following figure, which refers to the wall mosaic band n.242/d.)


Lesena 242/d. To reproduce exactly the figurative model of the pilaster, we have to determine complicated math processing twice [ and then they can be put together into graphic proceedings] : first to determine the perfect inscription of the hexagon into the six-pointed star [A-B-C-D-E]; secondly to determine the perfect inscription of the squares into the rhomboidal parts which are outside the six-pointed star [F-G-H-I]. [Design by G. Oddo - Digital elaboration]

If you look at the piece of floor of the low figure, you cannot but notice the extraordinary aesthetic quality of the whole. If you then think about the opportunity that this kind of study and research allows, you will better understand that our aim isn’t merely that of providing a historical-artistic documentation of some works, but, above all that one of providing archives ready to reproduce images in the wanted size [ an example is the second detail lower] and in so many versions that, if we dismantle or manipulate the figurative text, we can finally enucleate some important aspects.



Sector 14. The process of reproduction of each piece of floor is the perfect result of the support of digital programmes for the graphic design. We would, therefore, like to underline that our work consists in the remaking of the existing floors, not in their mechanical reproduction. That’s where the importance of our work lies. [Design by G. Oddo - Digital elaboration]

Usually, a regular-composed system of geometric figures can be reproduced by traditional and elementary methods, such as squared paper. But, if this type of reproduction is made by much more advanced and refined instruments, such as by digital programs for graphic design, the result is so perfect that those who work on it have the feeling of giving its original formal perfection again to the work, as it was still untouched by the passing of the time. So, between the real figure and the reproduced one there is the same qualitative distance that there is between what is roughly determined and what is not.

By alternating our point of view from the historical work of art to the digital one, we find ourselves like oscillating between two aesthetic perceptions; one founded on the perceiving of what is imperfect, and the other on the perceiving of what is perfect: one is the complementary part of the other and they serve each other for their mutual comprehension. In the first case, we have to face with the hardship of the creation but also with the deterioration of the existing work. On the contrary, as regards “ the perfect aesthetic perception”, we have that feeling of pure precision and integrity typical of what is freed by contingent elements.


Lesena 038/S. The mosaic figurative band is obtained by the aggregation of two modular square units, module A and module B, which alternate with regular intervals. The modules with the eight-pointed star are dominant units of the band. Right: the module A is made by 160 tiles. The numeration indicates the positions of each tile. The total is used to calculate the module fractionation index and the average area of the mosaic elements.


The overlay of geometric patterns on the modular device falls under this customary type of study. A first overlay shows the properties of the elementary geometrical figure of reference, in this case the square: the horizontal and vertical axes, the diagonals, the radial beam lines dividing the angle into segments of around 22.5°. A more advanced geometric study often determines the design of such an intricate geometric complexity as to require, for the readability of the graphs, the use of a plurality of several elaborative schemes.


St Luigi span [sector 7, plan of the pieces of the floor] subsector n. 13, northern view. The technological instrument, that is computer, provides a perfect, uniform and continuous version of the mosaic scheme which is the background of the four hares, avoiding cutting the panels to mould their profile. It also keeps alignments and angles and it proportions the size of the panels to the size of the operating field. [Design by G. Oddo - Digital elaboration]

It also may happen that, in spite of the technological support[ especially that one we use] and its great potential, the result is improper for some circumstances which don’t depend on our will. This may happen mostly on the pieces of floors rather than on wall parts, because of the course of the outlines of the floors. We are referring to the folding of the outlines and consequently to its eventual incompatibility between the figurative module of the mosaic scheme and the folding itself, just in that point and with that angle.


The stratagems of the mosaicist

We can notice one of the counterbalancing procedure, which consists in the contraction of the figurative module so that the mosaicist is able to fold the outline properly, in the second module of the floor sector 3. We are in the Antipresbyterium, also known as atrium of the choir.

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