The high altar retable of San Marco - the Pala d'Oro - is universally considered to be the most precious and refined expression of Byzantine genius and the cult of light, understood as the raising of man towards God. It glorifies the evangelist and contains his relics. It is bascially a Byzantine altar screen of gold, studded with hundreds of gems. They include 1,300 pearls, 300 emeralds, 300 sapphires, 400 garnets, 100 amethysts, plus rubies and topazes.
Pala derives from the Latin palla, cloth, sometimes decorated with images of saints and used to cover the altar or embellish its background during the church service. These cloths were then replaced by gold or silver - frequently found at least in Venetian lagoon area churches - hence the name Pala d'Oro (gold) or d'argento (silver). The most famous of all is the one in St. Mark's, ordered from Constantinople by the doge Ordelaffo Falier in 1102 and completed in 1105. It consists of 2 parts: the Pala d'Oro proper and the wooden container behind it. 
Since its origins it has been opened only during liturgical celebrations in the Basilica, a tradition that continues today. The rest of the time it is covered by another altar-piece known as "ferial", a painting on wood. The oldest of these was done by Paolo Veneziano and his sons in 1343-1345 depicting stories of St. Mark and other saints. It is now in the Church Museum. The present day one, the work of a late Gothic master, dates to the first half of the 15th century and may be admired on the rear side of the retable.

In the centre of the precious piece the majestic figure of Christ blessing is dominant, surrounded by the Evangelists holding open the book in which the words of holy scripture are replaced by gems, thus highlighting the preciousness of the word. Beneath Christ, Virgin Mary praying and, at her sides, the doge Ordelaffo Falier and empress Irene. 
Above Christ, the etimasia, the preparation of the throne of the Last Judgement, for God's second coming to earth, between two cherubim and two archangels. Above: the Crucifixion.
At the sides, in three registers one above the other, there are twelve prophets, twelve apostles and twelve archangels. Aligned above are almost all the celebrations of the Byzantine Church: from the left, the Annunciation, the Nativity, the Presentation at the Temple, the Baptism of Jesus, the Last Supper, the Crucifixion, the Descent into Limbo, the Resurrection, the Incredulity of Thomas, the Ascension and Pentecost. 
At the sides in a vertical position there are ten small pictures: on the left the salient events in the life of St. Mark and, on the right, episodes relating to his martyrdom in Alexandria and the transfer of his body to Venice. The great upper frieze from one of the three churches in the monastery of Christ Pantocrator in Constantinople shows the archangel Michael in the centre and six panels with Christ's Entry into Jerusalem, the Descent into Limbo, the Crucifixion, the Ascension, Pentecost and the Virgin Sleeping. The altar panel is completed by numerous enamelled medallions portraying saints worshipped by the Venetians.

Three phases may be identified in the history of this precious work: 

• The lower part dates to the time of doge Ordelaffo Falier (1102-1118). The enamels on the side frames, with stories of St. Mark, and on the upper frame with six deacons and the Christological celebrations of the liturgical calendar date to the same period, as does the central Pantocrator group.

• The upper part belongs to the second phase. The series of six Byzantine celebrations and the archangel Michael in the centre perhaps arrived in Venice from Constantinople after 1204.

• The third intervention occurred between 1343-1345 when, at doge Dandolo's behest, two Venetian goldsmiths were entrusted with the task of framing the whole within a Romanesque arch (upper part) and a Gothic arch (lower part), and distributing the 1.927 precious stones and gems.