The mosaic decoration of the entire upper part of the architecture of
St. Mark's - an area of around 8.000 square metres - is fruit of
one unifying idea.
Scholars agree that the grand iconographical plan of the interior
was already completed in the course of the 12th century. The mosaics
in the interior recount the events of the New Testament, with the
great message of Christian salvation.
The mosaics in the atrium, carried out afterwards, during the 13th
century, are a meditation on the Old Testament, in particular
the books of Genesis and Exodus, and are well located as
precursor of and preparation for the interior.
Interwoven with this main plan one identifies many others: the story of
the Virgin, the martyrdoms of St. Peter and St. Clement,
the events of St. John the Evangelist's life and those of John
the Baptist and St. Isadore, the great pantheon of saints
worshipped by the Venetians and, most important of all, the cycles with
the legend of St. Mark.
The gold background of the mosaics does not only give unity to
the mosaics themselves but, in accordance with the oriental conception,
has a precise symbolic value as the colour of the Divine, the image
of that light which, for the theologians and Fathers of the mediaeval
church, was God himself.