 For this he installed two large wheels just behind the doors through which the Magi procession appeared and disappeared, and on each of these wheels he mounted 12 large pierced metal sheets with glass inlays, one to show Roman numerals from I to XII and the other to show Arabic numerals from 0 to 55 in steps of 5.These were illuminated from behind by gas lamps, so that the numbers could be seen from the square below.During the Magi procession, the wheels were lifted away from the doors to allow the statues to pass through, and the temperatore changed the numbers manually.