In 1493 the Venetian Senate commissioned one Zuan Carlo Rainieri of Reggio Emilia to create a new clock for St Mark's Square, even though they had no idea where they where going to put it.
It took them two years before they finally agreed to arch over the passage leading to the Merceria, and build a tower, the Torre dell'Orologio, in the gap between the existing buildings. It was completed and unveiled on 1 February 1499.
Immediately above the arch are the two clock faces. The one facing the square shows the phases of the moon (still important to this day in a city so vulnerable to high tides), the time, and the positions of the sun and the major planets in the zodiac. The one on the back is simpler; it just shows the time.
On the second floor (either side of a Madonna and Child) is what some claim to be the first digital clock display in the world. This was installed in 1857 by the then owner of the clock, Luigi de Lucia. Before that there were doors through which figures of a herald angel and the three Magi would emerge and bow to the statue. They had to be wound by hand, hence Luigi de Lucia's decision to replace them.
Twice a year, on the feasts of the Epiphany and the Ascension, the digital wheels are swung out of the way and the old procession is reinstated.
On the roof, above the St Mark's Lion, is the Great Bell and two bronze figures of shepherds each 2.5m high, who hit the bell with hammers. These figures are referred to as Mori because of their dark colour. They also appear to have forgotten their underpants.
The Torre dell'Orologio was in private hands until 1998, when it was taken over by the City of Venice and subject to a heavy-handed restoration and internal modernisation.
It is now administered by MUVE and can be visited by guided tour only, bookable through their web site, see below.