ARCHITECTURAL STYLES - OWING. To its isolated position on the verge of Italy, and its constant intercourse with the eastern shores and islands of the Mediterranean, Venetian architecture was an independent development, though with many Oriental characteristics, having a character of its own quite unlike the styles employed in other Western countries. It was a very complex growth, in which the most diverse styles were absorbed and blended together in a very beautiful way. The various strands which, woven, as it were, together, combined to form the magnificent web of Venetian architecture were chiefly these, - (1) the Byzantine, itself a most complex mixture of older styles, blended together and vivified with new life in the hands of the skilful builders and craftsmen of Justinian's time ; (2) the Moslem as developed in the gorgeous mosques and palaces of Persia, Syria, and Egypt ; (3) the Gothic of northern Europe, and especially of France, with a secondary strain of Florentine influence, which, however, was more marked in the sculpture than in the architectures In the 11th and 12th centuries the Byzantine style was universally employed by the Venetians. The arches of this period are semicircular, usually much stilted. The sculptured ornament is of very great beauty, and is applied freely round arches, along strkig-courses, and in panels, with which the external facades were often thickly studded. According to the peculiar Venetian system of decoration, the walls were built in solid brick-work and then covered with thin slabs of rich and costly marbles. The columns, with their capitals and bases, were, as a rule, the only places where solid blocks were placed. This constant method of facing with thin slabs necessitated the use of special forms of mouldings and carvings, and thus, except in the solid capitals, no deep cutting could be employed ; therefore the mouldings of this period consist of small rolls, cantles, or flutings contrived to enrich the surface with the least amount of cutting into the thin marble.6 In the same way the sculptured bands are shallow in treatment, but full of the most vigorous grace, combined with the utmost spirit, in every line and curve, and. rich, with an extreme delicacy, in all the details. Flowing scroll-work of semi-conventional foliage, mingled with grotesque animals, birds, or dragons, is most connnonly used. As purely decorative sculpture, nothing could surpass the beauty of these early bands and panels. The round or arch-shaped or rectangular sculptured panels, used to stud the facades like rows of jewels, are of peculiar beauty and interest. Many of the designs are derived from the far East, and appear to be of Sasanian origin ; favourite motives arc eagles or dragons devouring hares or other animals, and peacocks treated in a conventionally decorative way, with their spreading tails forming a halo-like background to the body of the bird. Many of these panels are derived from the very ancient Assyrian subject of the sacred tree between two guardian beasts or birds; a common variety of this has two peacocks face to face drinking from a cup placed on a tall, pillar-like object, which recalls that on the lion-gate of Myceme. Many of these reliefs closely resemble the sculptured screens and altars of the 6th century in Ravenna, and are probably of the same date, though used to decorate buildings not earlier than the 12th century. The church of St Mark, especially, is a rich storehouse of these examples of early sculpture. Others of exactly similar style, which exist in the churches of Thessalonica and other Eastern cities, bear witness to the unity of early Byzantine art and its wide geographical range until the downfall of the Eastern empire. One striking feature in Venetian architecture of all dates clown to the 15th century is the constant use of the lentil moulding. This consists of a simple series of notehings, at once the easiest and the most effective way of enriching the thin facing-slabs when their edges were allowed to appear, as, for example, in those which lined the soffits of arches.

The influence of Moslem art is seen in the occasional use of the horse-shoe arch, in the very common ogee form which was almost universal in Venice from the 13th to the 15th century, and still more clearly in the fantastic rows of battlements, formed of thin pointed slabs of marble set on edge, which crowned the walls of nearly all the chief palaces of Venice in the 14th and the 15th century.

The 13th century was the time of transition from the round arched Byzantine style to the pointed arch with tracery, which in some cases was derived directly from the Gothic of northern countries. This is seen especially in the two great churches of the Dominican and Franciscan friars, SS. Giovanni e Paolo and S. Maria Gloriosa (lei Frani. These two stately churches resemble those built by the friars in other places in Italy,' and have little of the distinctively Venetian character of the contemporary domestic buildings. In the 14th and 15th centuries one peculiarity of Venetian Gothic is the way in which tracery is used to fill rectangular and not arched openings. The result of this is that the tracery itself has to support the mass of wall above it, whereas in the Gothic of other countries the tracery is merely, as it were, a pierced screen filling in a constructional arch, which carries the whole weight of the superimposed wall and roof. Hence the Venetian tracery, of which that in the upper story of the kcal palace is a typical example, is much thicker and heavier in construction.

In the latter part of the 15th century Venetian architecture began to lose its distinctively local character, though very beautiful examples of Early Renaissance were built by the Lombardi family and other architects, largely under the influence of Fra Ciocondo (see VintoNa).

In the 16th century, under the later development of the Renaissance, the Pseudo-Classic style was paramount in Venice, and Sansovine, Palladio, and others designed many costly buildings which had nothing specially Venetian in their style. This magnificent but dull and scholastic form of architecture reached its highest development in Venice, where it was later in degenerating into tasteless decadence than was generally the case elsewhere. Even in the 17th century good models of the Revived Classic style were built, especially by Longhena (see p. 155 below). After that the degradation of architecture and sculpture took place with great rapidity.

The periods of these styles may be roughly tabulated thus : - (i.) Byzantine, 7th to end of 13th century ; (ii.) Gothic, middle of 13th to c. 1160 ; (iii.) Early Renaissance, c. 1450-1520 ; (iv.) Classic, c. 1520-1320 ; (v, ) Extreme Decadence, c. 1600 downwards.

Mate•ials and Methods of Construction. - 1u. spite of its position on a number of small sandy islands in the lagoons, Venice was built upon firm and solid foundations, so that very few houses have suffered seriously from settlement. At a depth of 10 to 16 feet there is a firm bed of very stiff clay, and below this a bed of sand and gravel, and then a thin layer of peat. Recent borings for Artesian wells to a depth of about 1500 feet have shown a regular succession of these 'beds - clay, gravel, and peat - repeated again and again as far down as the borings have reached. The process implied in this geological formation seems still very slowly to be going on, and the present level of the square of St Mark has been raised artificially about 20 inches above the old brick paving shown in Gentile picture of 1496. A good example of the old method of forming foundations is shown in that of the great campanile of St Mark, c. 900 (see fig. 1). Here the builders dug down to the bed of stiff clay, and over the whole area of the footings of the tower drove in piles of white poplar, 10 to 11 inches in diameter, nearly touching one another. On the top of these a level platform was formed by two layers of oak trees (Quercus robur), each roughly squared, the upper layer being laid crosswise upon the lower one. The oak and poplar both grew along the shores close to Venice ; in later times, when the Venetian territory was extended, the red larch (Pines Larix) of Cadore and the Euganean Hills was largely used, as, for example, in the foundations of the dueal palace. In 18S5 the foundations of the campanile were examined, and both the oak and the poplar were found to be perfectly sound." On the wooden platform massive footings are laid, consisting of five courses

Throughout the 5liddle Ages the main walling of Venetian buildings was always of fine brick, usually a rich red in colour, made and fired in the kilns of Murano. In spite of its beautiful colour the brick-work was seldom left visible, the- whole wall-surface being lined with thin slabs of marble in the more magnificent buildings, or else coated with stucco, on which diapers and other decorative patterns were painted.

Before 1405 the mortar used in Venice was made of the white lime from the Istrian limestone, which possessed no hydraulic qualities, and was consequently very perishable. lint after that year, when the 'Venetians conquered Patina, they were able to get supplies of a strong hydraulic dark lime from Albettone, which formed a very durable cement or mortar, able to resist salt water and the destructive sea air.

One of the chief glories of Venice depends on its extensive use of the most beautiful and costly marbles and porphyries, which give a wealth of magnificent colour such as is to be seen in no other city in the world. In early thins none of these seem to have been obtained direct from the quarries, but from older buildings, either of Roman or early Byzantine date." Immense quantities of rich marbles were brought from the ruined cities of Heraclea, Ravenna, Altinum, and especially Aquileia. Under the Roman empire Aquileia contained great numbers of magnificent buildings, decorated with marbles and porphyries from Greece, .Numidii, Egypt, and Arabia. The gorgeous churches and palaces of the Byzantine emperors, enriched with rare marbles stolen from Greek and Roman buildings of classic times, were in their turn stripped of their costly columns and wall-linings by the victorious Venetians. Thus Venice became a magnificent storehouse in which were heaped the rich treasures accumulated throughout many previous centuries by various peoples. The principal varieties used in the palaces of Venice are - time red porphyry of Egypt and the green porphyry of Mount Taygetus, red and grey Egyptian granites, the beautiful lapis Atracius (verde alnico), Oriental alabaster from Numidia and Arabia, the Phrygian pavonazzetto with its purple mottlings, cipollino from Carystns, and, in great quantities, the alabaster-like Proconnesian marble with bluish and amber-coloured striations.' Till the 14th or 15th century the white marbles used in Venice were from Greek quarries - Parian or Pentelic - being all (like the coloured marbles) stolen from older buildings, while in later times the native marble of Carrara was imported. Large ..quantities of red Verona marble were used to form moulded frames round panels of white sculptured marble. The greater part of these costly marbles seems to have been imported in the form of columns, immense numbers of which were sawn up lengthways into long thin slabs for use as wall-facings. Other columns, usually those of the most precious marbles, were sawn across, and thus the roundels were produced which stud like jewels the facades of many cf the palaces (see fig. 6). Thin slices sawn front the same column were reversed and placed side by side, so that the natural mottlings formed a regular sort of pattern. Very rich and complicated designs were produced by placing four slabs together to form one large pattern, repeating from one centre. The whole interior of St Mark's is decorated in this magnificent way, very large areas being covered with the same pattern recurring again and again. TIms no attempt was made to disguise the fact that the marble was only a thin surface decoration of no constructional importance. TIM fact that many slabs had been cut from one block was frankly acknowledged by the formation of these "cut and reversed " patterns, nor is there any attempt to conceal the bronze clamps which hold the slabs in their places.

The facades of the chief palaces of Venice down to the end of the 15th century were wholly covered with these magnificently coloured marbles. But that was not all ; a still greater splendour of effect was given by the lavish use of gold and colour, especially the costly 'ultramarine blue. Very frequently the whole of the sculpture, whether on capitals, archivolts, or frieze-like bands, was thickly covered with gold leaf, the flat grounds being coloured a deep ultramarine so as to throw the reliefs into brilliant prominence. The less magnificent palaces were decorated in a simpler way. The brick surfaces between the windows and other arches were covered with fine hard stucco, made, like that of the ancient Romans, of a mixture of lime and marble dust. The whole of this was then decorated with minute diapers or other geometrical ornament in two or three earth colours, especially red, yellow, and brown ochres. Very few examples of this form of decoration still remain, owing to the corrosive action of the sea air. One notable example, dating from the 14th or 15th century, has a rich pattern formed by a series of adjacent quatrefoils, with half-figures of cherubs in the intermedi- ate spaces, covering the whole flat surface of the wall. A few faded patches are now all that is left.

With the early years of the 16th century and the hater development of the Renaissance totally different methods of architectural decoration superseded the use of precious marbles and delicate repeated ornament in colour. The Pseudo -Classic buildings of Sansovino, Palladio, and their schools were either built of white stone or marble, quite unrelieved by colour, or else stuccoed facades were treated simply as a ground on which to paint large frescos with figure subjects, not designed with any sense of the true principles of architectural decoration. These frescos, which covered the otherwise unornamental facades of many of the 16th-century palaces, were often the work of the greatest painters, from Giorgione to Tintoretto ; but the pictures, though no doubt beautiful in themselves, were obviously quite out of place on the facade of a house : the colossal groups dwarfed the building they were painted on, and were far inferior in decorative effect to the simpler patterns of earlier times. These, too, have mostly perished: on the fondaco2 of the Germans, once covered with frescos painted jointly by Titian and Giorgione, only traces of two figures now remain. One of the best-preserved series of these exterior frescos is that inside the cloister of S. Stefano, painted by Pordenone, which has naturally suffered less than the very exposed facades on the Grand Canal.

Mural, of St Mark. - This church stands quite alone among the buildings of the world in respect of its unequalled richness of material and decoration, and also from the fact that it has been constructed with the spoils of countless other buildings, and therefore forms a museum of sculpture of the most varied kind, nearly every century front the 4th down to the latest Renaissance being represented in some carved panel or capital, if not more largely.

The splendid columns of St Mark's, which Mr Ruskin in the Stones of Venice speaks of as being or alabaster, really are of Proconnesian marble, and are so described by various early Byzantine writers. According to Vitruvius (ii. 8), the magnificent palaces of Crresus of Lydia and Mausolus of Eancarnassus were chiefly adorned with Proconnesian marble.

During the early years of Venetian history the site of the present church and square of St Nark was a large grassy field,with rows of trees, divided by a canal (which no longer exists), and containing two churches. One of these, dedicated to St Theodore, the old patron saint of Venice, stood on the site of the present church of St Mark. The other, that of S. Geminiano, was a little to the northwest of the great campanile. Fig. 3 (below) shows its position, and also the site on which it was rebuilt by Sebastiano Ziani (1173-79), when he pulled down the original church in order to extend the square westwards. In the 16th century it was again rebuilt by Cristoforo del Legname and Sansovino, and was destroyed hi 1805 by Napoleon I., to make room for a new block to unite the two palaces of the procurators. The grassy camps where these churches stood was the property of the abbey of S. Zaccaria. At its eastern extremity a small palace was built for the doge about 810, when Venice first became the chief ducal place of residence under Angelo Partecipazi o.

According to the chief early chronicles, the body of St Mark was secretly brought away from Alexandria and carried to Venice in 828, the church where he was buried having been pilled down by the Moslems in order to build with its materials a palace at "Babylon," as old Cairo was then called. After the arrival 'of his relics, St Mark became the patron saint of Venice in place of St Theodore, and his bones were laid in the "confessio " of the small private chapel of the ducal palace.' This chapel, however, soon lost its private character and became the chief church of Venice, though not the cathedral church of the patriarch. The small ducal chapel of St Mark was burnt in 976, together with the rest of the palace, during the insurrection against Doge Candiano IV. : it was rebuilt on a larger scale by his successor, Pietro Orseolo, and the

The genera] scheme of decoration is the following. The whole of the domes and vaults, and the upper part of the walls down to the level of the floor of the triforiiim, are completely covered with mosaics of brilliant glass tesserse, the ground being in most cases of gold. Below this every inch of the surface of the walls and arches is covered with richly coloured marbles, porphyries, and alabaster, relieved by pure white marble, sculptured in panels, string courses, and the like. The various marbles are arranged in broad upright bands, alternating so that one colour enhances the effect of that next to it. For example, the nave wall in the north aisle is faced thus, - (1) verde antic°, (2) Proconnesian, (3) red broccatello of Verona, (41 Proconnesian, (5) magnificent Oriental alabaster, (6) Proconnesian, and (7) verde antic° ; below these is a narrow band of red Verona marble, and then a plinth-moulding of Athenian white marble, which rests on the seat of panelled red marble that runs all round the interior of the nave and transepts. The large columns between the brick piers, six in the nave and eight in the transepts (see fig. 2), are monoliths of fine Proconnesian marble, veined with greyish blue and anther, and the great brick piers are faced with thin slabs of the same material. This facing and most of that throughout the church are made of ancient columns sawn into slices.

The eastern crypt or confessio extends under the whole of the choir behind the rood-screen, and has three apses like the upper church. The body of St "Mark was originally placed here, but is now within the high altar of the upper church. Below the nave is au older crypt, the existence of which has only recently been discovered ; it is not accessible, having been filled in with earth and rubbish at. a very early period.

l'he choir, which is raised about 4 feet above the nave, is separated from it by a marble rood-screen, formed of ancient columns, bearing a straight architrave surmounted by fourteen statues, viz., St M ark, the Blessed Virgin Nary, and the twelve apostles. It extends across the aisles, forming a north apsidal chapel of St Peter and a southern one to St Clement. The rood-screen is signed as the work of the Venetians Jacobello and Pietro Paolo, sons of Antonio delle14Iasegne, 1394-97. The rood itself is of silver, dated 1394 and signed "Jacobus Magistri Marci Benato de Venetiis." The workmanship both of the silver crucifix and of the fourteen statues is of no great excellence. In front of the screen stand two very large amboues or pulpits, one of porphyry and the other of verde antic°. In the northern ambo is a lofty patriarchs throne under a metal domed canopy, curiously like a pulpit in a Moslem mosque. There are fine marble baldacchini, supported on columns of precious marbles, over the high altar, two in the transepts, and one on the north side of the nave. No less than five hundred columns of porphyry and costly marbles are used to decorate the church, especially on the west front. Some of those inside the atrium have no constructional use, but are only set against the wall for the sake of their beauty and value.

A whole volume might be written on the sculptured capitals, panels, screens, and other features of the church. A great part of these are the spoils of other churches, especially from the East ; much of the sculpture, as, e.g., the parapets along the triforium gallery, dates from the 6th century or even earlier.' In the richly carved capitals every style from the 4th to the 12th century is represented, many of them being marvels of delicacy combined with extreme spirit of execution. Some of the larger caps are partially covered with a rich basket-work pattern completely under-cut with great technical skill ; others have vine or acanthus foliage treated with vigorous realism ; and a large number have the revived Byzantine treatment of the classic Corinthian or Ionic capitals, with variations showing the richest power of invention and originality. In addition to the elaborate sculpture, sonic of the capitals are decorated with inlaid patterns ; and many of the mouldings, such as the capping of the triforium screen, are also ornamented in the same way. This use of inlay is almost peculiar to St Mark's, as is also the method of enriching sculptured reliefs with backgrounds of brilliant gold and coloured glass mosaics, producing an effect of extraordinary magnificence.5 The exterior is no less magnificent than the inside, the whole = facades being covered with sculpture, mosaic, or slabs of rich marble. The west facade especially is a marvel of lavish expenditure both of labour and of costly material. The design consists of two main stages, the lower one being formed by the atrium, a 12th-century addition, in front of the older facade. Each stage is divided into five great arches, decorated with richly sculptured archivolts and with tympana filled in with mosaic pictures. Only one of the original mosaics now exists on this front ; all the rest have been destroyed and replaced by others of very inferior style in the 17th and 1Sth centuries. The one original mosaic is over the northernmost of the four doorways into the western atrium ; its date is about or soon after 1220. It is of great decorative beauty, and its subject - the translation into the church of the body of St Mathis of great interest from its careful representation of the west facade of the church as it was at the be-ginning of the 13th century. It shows the original form of the upper part of the facade before the addition in the 14th century of the large ogee gables with elaborate crockas, alternating with statues, and intermediate pinnaeled canopies placed between the five great arches of the upper story. It also shows the marble screen-work which once filled the great central west window, the whole of which is now missing, only the columns which supported it being left.° Similar filling-in still exists in some of the large side windows. The lower or atrium story is enriched with a wonderful collection of columns of precious marbles and porphyries arranged in two tiers. The sculptured archivolts, with foliage mixed with figures or subjects in relief, are of great beauty and variety. They are all carved in fine white Athenian marble, and were once gilt, as appears to have been the case with nearly all the sculptured. ornaments of St Mark's. This extensive use of gold is clearly shown in Gentile Bellini's picture. The top of the atrium forms a wide upper gallery communicating with the interior at the triforium level. In the centre of this gallery stand the four colossal bronze horses, from sonic Grieco-Roman triumphal quadriga, which were brought to Venice after the conquest of Constantinople by Enrico Dandolo in 1204.7 The roofs, including the five great external domes over the nave, choir, transepts, and crossing, are all covered with thick sheets of lead. The internal domes, like the rest of the vaults, are of brick, the external domes being of wood. The drums on which the outer domes rest are hound round with strong iron bands, which were added by Jac. Sansovino in the 16th century. The round-headed windows in the drums were once filled in with pierced screen-wo•k of marble, some examples of which still exist in the western atrium, --an interesting relic of the method of filling windows employed at a time when glass was but little used.

The mosaics in the interior are among the finest and, from their variety of date, the most interesting series in the world ; those dating from the 12th and 13th centuries are of special beauty. The earliest appear to be those on the five great domes, probably executed before 1150. On the nave dome the subject is the Descent of the Holy Spirit : tongues of fire radiate upon colossal figures of the apostles, and below them, on the drum of the dome, is a second series of figures representing the various nations of the world who were converted through the inspired teaching of the apostles. On the dome over the crossing is the Ascension of Christ, with bands of large figures of the Apostles, and below them the Virtues. On the choir dome are a half figure of Christ and a series of the Prophets. In the main apse is Christ in Majesty. The transept domes have series of Saints and Doctors of the Church. All have explanatory inscriptions. The whole of the rest of the vaults and the upper portion of the walls are covered with mosaic pictures, of which a mere catalogue would occupy many pages. In the atrium the subjects are taken from the Old Testament ; these date from c. 12001300. In the baptistery' are the life of St John the Baptist and scenes from the life of Christ ; on the first dome (westwards) is Christ in Majesty over a series of baptismal scenes and the Greek Doctors ; on the second dome, Christ surrounded by Angels. On the barrel vault of the chapel of St Isidore is a very beautiful series of mosaics, with scenes from the saint's life and other subjects, executed in 1355, soon after the completion of the chapel. In the sacristy is a fine series of 15th-century mosaics, and in other parts of the church there are mosaics of still later date, some of them from cartoons by Tintoretto and other Venetian painters of the decadence. These later mosaics are not desii,med with any real sense of the special necessities of mosaic work, and are all very inferior in decorative effect to the simple Byzantine style from the 12th to the 14th century.

Most of the existing mosaics of the earlier periods have suffered very seriously from "restoration," a process which is still going on, with most fatal results to the interest and real value of the mosaics. The exterior marble facing and much of the sculpture have within recent years been completely renewed in the most tasteless way, - the fine slabs of rich Oriental marbles having been largely replaced by cheap greyish. Carrara marble of the worst quality, quite devoid of the fine colours and rich veinings of the original slabs. The same fate now threatens the magnificent mosaic pavement of St Mark's, the surface of which has sunk into a succession of wavy hollows, owing to the settlement of the vaulting of the crypt below on which the nave paving rests.5 The original part of the mosaic. floor probably dates from about the middle of the 12th century. The nave pavement of the cathedral at Murano, which is exactly similar in style, Materials, and workmanship, has an inscription dated 1140. The pavement of St Mark's consists partly of opus Alexandrinum of red and green porphyry mixed with some marble, and partly of tesselated work, made both of glass and of marble tessera,. The two methods are obviously of the same date, as in some eases both processes are used in the same design. The opus Alexandrinum is very similar in style to that in sonic of the basilicas of Tbessalonica, and also those in Rome, most of which are of about the same date, the 12th century. The designs executed in mosaic tessera; are of several different styles, sonic being taken from the mosaics of Roman classical times, while others, with large panels of peacocks on each side of a vase, eagles or lions devouring their prey, and the like, are copied from Byzantine reliefs of much earlier date than the 12th century.2 The originals of many of these are to be seen in the sculptured roundels which stud the facades of Byzantine palaces in Venice. A great part of the pavement of St Mark's has been repaired and renewed at various times, from the 14th century down to the present time ; consequently a great variety of styles and materials occurs mixed with the original parts. The pavement in the north aisle was renewed in the most clumsy and spiritless fashion about twenty years ago, and it is much to be feared that a similar fate awaits the rest of these priceless mosaics.

One of the great glories of St Mark's is the most magnificent gold retable in the world, most sumptuously decorated with jewels and enamels, usually known as the Pala d'Oro. It was originally (according to the Venetian chronicles) ordered in Constantinople by Doge Pietro Orseolo I. in 976 ; and an inscription in enamelled letters added in 1345 records that it was brought to Venice and partly renewed by Doge Ordelafo Falieri in 1105 ; in 1209 it was again repaired and enlarged by Doge Pietro Ziani ; and finally in 1345 Andrea Dandolo reset the enamels in new framework, mat added some minute gold canopies and other decoration of Gothic style. In the 19th century it was thoroughly repaired and the stolen gems replaced by new ones, easily distinguishable from the original jewels by being cut in facets, not " en cabochon " after the old fashion. This marvellous retable is made up of an immense number of microscopically minute gold cloisonné enamel pictures, of the utmost splendour in colour and detail. The enamels are partly translucent, allowing the brilliant gold backing to shine through the coloured enamel. The subjects are Christ in Majesty, figures of Archangels and Angels, and a very large number of single figures of Prophets and Saints, as well as many scenes from the life of Christ and of St Mark. No description can do justice to the splendour of effect produced by this gleaming mass of gold, jewels, and enamels ; the delicacy of workmanship of the latter is only equalled by two Textus covers, also in gold cloisonné, now preserved in the treasury of St Mark, which also possesses a magnificent collection of church plate of all sorts, such as large chalices and patens in crystal and agate, reliquaries, candlesticks, altar frontals, and other kinds of church furniture, all of the most precious materials and wo•kmanship.4 Two silver frontals of the 14th century, now used for the high altar of St Mark, originally belonged to the cathedral of Venice, S. Pietro di Castello.