Bernini's first work at St. Peter's was to design the baldacchino, a pavilion-like structure 30 metres (98 ft) tall and claimed to be the largest piece of bronze in the world, which stands beneath the dome and above the altar. Its design is based on the ciborium, of which there are many in the churches of Rome, serving to create a sort of holy space above and around the table on which the Sacrament is laid for the Eucharist and emphasizing the significance of this ritual. These ciborium are generally of white marble, with inlaid coloured stone. Bernini's concept was for something very different. He took his inspiration in part from the baldachin or canopy carried above the head of the pope in processions, and in part from eight ancient columns that had formed part of a screen in the old basilica. Their twisted barley-sugar shape had a special significance as the column to which Jesus was bound before his crucifixion was believed to be of that shape. Based on these columns, Bernini created four huge columns of bronze, twisted and decorated with olive leaves and bees, which were the emblem of Pope Urban.