The ciborium is at the centre of the presbytery, the most sacred part of the church which includes the high altar with the marble sarcophagus containing St. Mark’s body, transferred here from its ancient place in the crypt.
The antique green marble ciborium stands on four columns in oriental alabaster embellished with historical episodes from the gospels (13th century).
There are ninety scenes, each with an inscribed comment. The rear left column has episodes from the life of the Virgin while the front left column has episodes from the lives of the Virgin and Christ. The font and rear right columns have episodes from the life of Jesus.
The four columns have been a subject of debate, still not resolved, regarding chiefly their date and place of origin.
The ciborium was erected above the high altar in St. Mark’s – where it remains today – on an uncertain date in the first half of the 13th century, probably in the 20’s.
On the edge facing worshippers there is a statue of Christ between those of St, Mark and St, John while behind, towards the apse, the Redeemer (1751) between St Mark and St. Luke, a 13th century work.
Debate on the ciborium has chiefly concerned the dating and origin of the four columns, precious columns used to support the baldachin vaults. The bas-reliefs that decorate them, though different in certain respects, are substantially unitary and can only originate from one production centre, even though they may have been created by artists of varying value. Recycled many times, the ancient columns are one of the most significant examples of early Byzantine figurative sculpture that have come down to us, both for the richness of the Marian and Christological cycles and the extraordinary quality of the work.
The four monolithic shafts in oriental alabaster, worked in pairs by an outstanding Maestro with less able helpers, are divided into nine sections separated by horizontal strips which are in turn divided into nine small arches containing one or more figures in high relief.
The dark background of the niches gives an almost total plasticity to the scenes. In the 324 niches there are an overall 108 scenes with one or more figures representing the life of the Virgin and the life and passion of Jesus Christ. In several detailed cycles, set out in a horizontal or vertical reading sequence, there are individual episodes from the canonical and apocryphal Gospels.
The rear left column shows thirty scenes dealing with the life of Mary, from the Sacrifice of Joachim to the Consultation of the priests on the future of the Virgin at twelve years. The sculptor has faithfully followed the descriptions in the Greek version of the early apocryphal gospel of James. The sequence of twenty-six scenes on the front left column begins with the Annunciation to Mary and continues with events from the youth of Jesus and, among other things, various stories of miracles and healing. These episodes, depicted with extraordinary vivacity, refer on the one hand to the early apocryphal gospel of James and on the other to the canonical Gospels, particularly to John.
The sculptural cycle continues on the rear right column with twenty-eight scenes illustrating the teachings and miracles of Jesus as recounted in the Gospel of St. Luke.
Lastly, the front right column illustrates twenty-four scenes from the passion of Jesus Christ.
Of particular interest is the extraordinary Crucifixion in which the symbol of the mystical Lamb takes the place of the figure of Christ.
Comparison at stylistic level with the ivories of the Eastern Roman Empire, and with 6th century sculptures still in Istanbul today, has permitted dating the work to the period of Emperor Anastasius I (491-518). The Latin inscriptions carved in the strips, often misleading with regard to interpretation, were added at the period of re-adaptation of the sculptural group to new arrangements in Venice in the 13th century.
The ciborium is the actual heart of the church and achieves its maximum communicative value when, on the occasion of celebrations held in honour of the saint, the sarcophagus with its relics is freed from the grilles enclosing it and covered with red roses, and the Pala d’oro (the altar retable) shines towards the worshippers.