The Clock Tower, stands behind the Palazzo Cavarretta on Via Torrearsa, in Trapani (TP).
It was built around the fourteenth century, marking the boundary between the original nucleus of the fortified city and the expansion to the west of the Aragonese period. Its access was allowed by the presence of the Porta Oscura, which still exists today, despite the transformations suffered as a result of the construction of the facade of the aforementioned building, built in 1678.  In that year the Tower underwent changes, with the amalgamation to the Palace of the room above the arch and the construction of the internal wooden staircase, to allow access to the old clock, located on the top floor .
In 1825 the clock of the tower stopped working, leaving the role to the new clocks placed to crown the facade of the Senate Palace. 
In 1827 two bronze bells were placed on top of the Tower. 
The latter, with a square plan, does not have a precise architectural style. In fact, at the wall level it shows no decorations. Presenting only on the facade overlooking the street Torrearsa , two circular dials with a clock above the calendar, a plaque and four holes that constitute two windows in the clock room and two circular windows without window frame.
The astronomical clock is one of the oldest in Europe and was designed and built by the Trapani master Giuseppe Mennella in 1596, commissioned by the Jurors . The marble used for its realization was extracted from the quarry Rizzuto (Valderice) and blends perfectly with some inserts in lead, handmade, with the edge in blue stone depicting the sky. 
It is formed by two circular dials : the "Sun" Quadrant and the Lunario . The large hole in the center of the Moon represents Planet Earth. 

SUN QUADRANT

Inside the dial of the Sun there are two hands: the one with the lily tip marks the 24 hours; the Sun hand, instead, reproduces the solar motion through the Zodiac, indicating through the signs of Aries, Libra, Cancer and Capricorn, Equinoxes and Solstices, as well as the alternation of seasons: 

1 Aries indicates the Spring Equinox;
2 Libra indicates the Autumn Equinox;
3 Cancer indicates the passage of the summer solstice;
4 Capricorn indicates the winter solstice.

MOON QUADRANT

In the underlying Lunario , the hand with the disc of the Moon indicates , counterclockwise, all phases from New Year’s Day to decrease : from the new moon to the waning moon. The second hand, instead, indicates the lunar month, that is the time span that the moon takes to complete a complete cycle : 29 days , 12 hours , 44 minutes and 3 lunar seconds. 
There are some lunar positions represented : 
1. the new Moon (or conjunction or new moon phase);
2. crescent moon;
3. the first quarter;
4. increasing gibbos;
5. full moon (or opposition or full moon phase);
6. falling gibbos;
7. the last quarter;
8. waning moon.