Constructed in the 13th Century, the Zytglogge tower is a landmark medieval tower in Bern. The tower is considered one of the old city's most recognizable symbols and tourist attractions. Most notably, the Zytglogge is home to a 15th Century astronomical clock. It is also part of the UNESCO World Cultural Heritage site. In the past, it has served as the city's guard tower, clock tower, prison, and civic memorial. The Zytglogge was constructed sometime around 1220. Initially it served as the gate tower of the city's western defenses.
Upon its completion, the building was a meager 16 meters tall. Officials added height to the tower in 1275 raising it to a total of 23 meters tall. This expansion took place because of the increased growth of the town, making it impossible for the tower to stand above surrounding houses. In 1344, the Zytglogge was transformed into a female prison housing women who had been convicted of sexual relations with clerics. Unfortunately, during the Great Fire of 1405, the tower's interior burn out completely. The damage required severe structural repairs that were not fully completed until a final restoration in 1983. Stepping back, the prison was abandoned during the 15th Century and a clock was installed for the town. The clock, accompanied by a bell cast in 1405, dubbed the Zytglogge (time bell) its current name. Also in the 15th Century, the Zytglogge garnered a new lantern, a new stair tower and four decorative corner tower decorations. The tower's clock was completely rebuilt between 1527 and 1530 by Kaspar Brunner. Built in the form of an astrolabe, the astronomical clock serves as the towers largest attraction.
The clock is backed by a projected planisphere separated into three zones in the light blue sky of day, a deep blue sky of dawn, and the blackened sky of night. The primary hand of the clock indicates the time of day based on its location on an outer ring of 24 golden Roman numerals. The clock also boasts a rete's calendar dial and a moon dial that depicts the current moon phase. Surrounding the clock is a painted frieze that depicts five deities from classical antiquity. Each represents a day of the week and planet per Ptolemaic cosmology. In order, they are Saturn with sickle and club for Saturday, Jupiter with thunderbolts for Thursday, Mars with sword and shield for Tuesday, Venus with Cupid for Friday, and Mercury with staff and bag for Wednesday. In all, there are two clock faces. One faces east and the other west. The Zytglogge's exterior is stunning to say the least. The current overall height of the tower is 54.5 meters. The tower sports late Gothic cornice under the roof and a stair tower. The exterior of the main body of the tower is constructed of alpine limestone. A three-story tower shaft adjacent to the main body features sandstone. Additionally, the tower's two-story attic is covered by sweeping, red-tiled, late Gothic spire and two spire lights. They are also crowned by ornamental urns featuring pinecone knows reconstructed in 1983.