The bell tower of Vilnius Cathedral is one of the city's main symbols and an important part of the complex of the Cathedral and the Lower and Upper Castles. Its history goes back to the mid-13th century: the defensive tower that stood here became a bell tower in the 16th century and took on its present appearance at the beginning of the 19th century. At the top of the building the city's oldest clock keeps time, the bells call to Holy Mass, an interactive exhibition presents the tower's history, and visitors are rewarded with impressive views of Vilnius. In the 13th century the tower was part of the defensive wall. Almost the entire ground floor of this building has survived to this day. The bell tower's walls are between 2.8 and 4 m thick. Over its history the bell tower burned more than once, and you can still see traces of the biggest fires – melted bricks and blackened stones. Besides the historic masonry, inside the bell tower you can see equally impressive 19th-century wooden structures and climb the stairs of that period. The cathedral's old bells were lost in various disasters; only two have survived, which strike the hours of the clock. So in 2002 the Archbishop of Cologne, Joachim Meisner, gave Vilnius Cathedral six newly cast bells. According to an old tradition, every church bell has a name, a symbolic sign and a Latin inscription. The large bells, weighing from 475 to 2,595 kg, now ring to mark the beginning and end of the day, call to Holy Mass and sound during solemn ceremonies in Cathedral Square. The cathedral bell tower clock is the oldest in the city. Its mechanism was installed in the tower in 1672. It needed a major repair only once, in 1803. The townspeople are helped to keep track of time by bells cast by the renowned masters Jan Delamars and Gustav Mörk, which ring every quarter and every hour. At the top of the bell tower you can see two surviving old clock faces. The bell tower is 52 m high, or 57 metres including the cross. Visitors can climb to the top floor (45 m), where an impressive panorama of the city opens up: the buildings of the Old Town, Gediminas Avenue, the Church of St Peter and St Paul, and a clear view of the sculptures adorning the Cathedral. For those who love modern technology, or who cannot climb to the top of the tower but would like to enjoy the views of Vilnius from up there, there is a virtual tour: you can control the cameras installed at a height of 52 m yourself.