The exterior of St. Mark’s features, in the upper part, the profile of the raised cupolas, wooden structures covered with sheet lead which were superimposed in the 13th century on the original brick cupolas. The profile of the faï¿½ade is enclosed by the Gothic crowning with aedicules, statues and floral decorations done between the 14th and 15th centuries by Nicolï¿½ and Pietro Lamberti and other Tuscan artists.
The lower body of the basilica, initially intended to remain in plain brick, was covered with marble along the sides where the north, west and south facades open out. This took place after the 1204 conquest of Constantinople when great quantities of precious oriental marbles, columns, capitals and reliefs were brought from the capital city of the eastern Roman empire, giving the Venetians the idea of decorating the three facades in a precious manner. The three faï¿½ades of St. Mark’s, North, West and South – to the East the apse was incorporated into the ducal palace – were conceived in a very different way from the viewpoint of their functions and therefore also of their decoration.
The west facade is divided into two orders by the terrace overlooking the famous bronze quadriga which was also brought from Constantinople. The main frontage of the church is punctuated by four great 12th century portals and the window of the Zen chapel. For each of these there is a corresponding lunette in the upper register. The most important is undoubtedly the main portal, a masterpiece of 13th century sculpture. Some sculpted Byzantine slabs are set into the 13th century marble covering: St. George and St. Demetrius, the Annunciation and the Labours of Hercules.
The south facade in ancient times included the “sea gate”, a great portal that issued onto the western atrium directly from the pier. In the 16th century this opening was closed by a marble transenna for internal construction of the Zen chapel. Marble facings and columns with numerous fragments of 13th century decoration also embellish the architecture of the Treasury, between the church and the ducal palace. The porphyry sculpture of the Tetrarchs is set on the corner, and before the baptistery door there are two richly decorated pillars said to have come from Acre but actually brought from Constantinople.
The north facade, with the same scheme as the other two, overlooks the piazzetta dei leoncini. Though it appears less rich in decorative elements it has some fine 13th century slabs (Christ and the four evangelists) near the gate of flowers which in turn is topped by an elegant sculpture with a Nativity scene.