The Torre dell' Orologio (Clock Tower), which stands in the north side of the Piazza San Marco, was designed and built by Mauro Codussi in the last decade of the 15th century.
The clock, which was hailed as the most complex astronomical device of its day, was constructed by Gian Paolo Ranieri and his son Gian Carlo, two clock-makers from Reggio Emilia. The clock-face shows the hours in Roman numerals; the hand takes the form of the sun. The inner ring depicts the signs of the Zodiac, while in the centre the various phases of the moon are recorded.
Above the clock is a tabernacle with the Virgin and Child. Originally, on the hour, figures of the three Magi led by a trumpeting angel, would emerge from the left door and process and bow before the Madonna before disappearing through the right door. This now happens only twice a year, on the feasts of Epiphany and Ascension. In 1858 two small drums, which display the hour in Roman numerals and the minutes in Arabic numerals, were inserted into the doors. This was done to make it easier to read the time from the piazza below.
Above the Leone Marciano hangs a great bell, which was cast in 1497. It is struck every hour by two giant bronze jacks, known as the two ‘Moors’.